In the 2023 movie The Killer, there is a scene (around 50:39) where The Killer (Michael Fassbender) parks his car in front of a house, and puts up a windshield sun shade that has "Need help please call police" written on the inside.
Is this a common thing in American rentals? What is the purpose of this?
It seems It used to be.
A quick Google search ends up with lots of 'vintage' and '1980s's references and pictures.
A 1989 Chicago Tribune article says this:
In the last five years, the accordion-pleated shades have popped up in cars from Valley Forge to the San Fernando Valley, from Key West to Cape Cod. They`ve become as much parts of the landscape as bumper stickers. Garfield and Odie, Batman, the California Raisins, ALF, Disney characters, women in bikinis, the Chippendales male strippers all can be yours for about $2.99. On the flip side of nearly every shade is the message, ''Need Help; Please Call Police.''
https://www.chicagotribune.com/news/ct-xpm-1989-08-20-8901060036-story.html
I would say that because they were so common when the director or the writer would have been growing up, that it's pretty much etched in their memories - and might well have been thought of as a nice touch to include.
Addressing other points (made in comments):
Is this a common thing in American rentals?
Not that I have seen, though it may have been part of an accessory pack. Especially in the sunshine states where the vehicle might have been exposed to the sun in a parking lot all day every day, then a cover may have been used to preserve the plastics (dashboard, steering wheel, etc). Whilst parked it can also help to keep the interior a little less hot by reflecting direct sunlight.
What is the purpose of this?
The 'help' part is a request for assistance (whether a breakdown, or more serious incident). These were common in the days before mobile cellular was available to everyone, and the distance to the next public phone might be quite far, or was unknown, so this would be the next best request assistance notice - usually in the form of a passer-by that might make note of it and call the emergency services to inform them of the notice.
Advertisers noticed the other side being blank, so this was utilized as advertising space.
So, before changes were made to vehicles (and society in the form of mobile communications) that made these less relevant, they served the purpose of keeping the dashboard and vehicle internally cool in a hot sunshine environment, a request for assistance notice, and advertising space. In the case of the movie it was also added privacy.
I caught something else:
The sun shade did not come with the rental. It was bought in the supermarket (Breaux Mart, found in New Orleans, not Florida...), along with the pack of meat, liquor, sleeping aids and other items. So, I guess to answer the question - no it is not supplied with rentals, so one needed to be bought.
These sun shades (in one form or another) were super common back in the 80s-90s in the sunnier parts of the US. The front had some sort of graphic design and the back usually had some variant of the "need help" message written on it. The general idea is that if you got stranded somewhere, you'd display that side of the shade. A passer-by could tell that you weren't simply a parked car and could call for assistance or stop and help. The other options available at the time were to abandon your vehicle and walk to get help (very slow, and not even feasible in many cases), or to stand on the side of the road and try to flag down a passing car (dangerous, low chance of success).
I always got the feeling that message was an afterthought. As if someone at the manufacturer saw the blank backside of the sun shade and thought "what should we do with this unused space that nobody ever sees?" Only marginally useful, but better than just leaving it blank, I suppose. I'd be curious to learn how many/few people actually used that side for its intended purpose and successfully received help.
You ask about rentals. I wouldn't say that that these types of shades were common in rental cars, but they weren't unusual in some parts of the country. The front might have the rental company's logo and phone number, or a message from a local organization that printed them up and "donated" them to the rental company (I recall seeing some with info about a local museum, or a "buckle up for safety" message). These shades weren't particularly good-looking but they were surprisingly effective at keeping the car cool. Rental companies would prefer that you used the shade because it also protected the dashboard from direct sunlight. The UV light in sunlight will cause many different materials to deteriorate, fade, or become brittle. I remember many cars from that era whose dashboards were faded, cracked, and peeling after years of being parked in the sun. Using the shade meant the rental car looked new for longer and helped preserve the resale value.
It's not really common, but not weird either. Think of bumper stickers. Some people love them and collect them, some dispise them. Same with sun visors, or tee-shirts with "funny" messages.
A quick search will show you hundreds/thousands of images/goods with this kind of message. You have some for the small sun visor, some for the windshield. There were also personal visors, but as a magazine once wrote:
An item of clothing that was designed for golfers and grannies from Florida was never really going to hold a place in fashion history
Such sun shades did used to be common, or at least something it was common to see, although not everyone had one. They can be double-sided. Ones with "call police" on one side would have something else on the other side for everyday use, the kinds of images or designs the other answers are describing.
(The article blobbymcblobby quoted does briefly mention this, and says it was very common to have a request for assistance on the flip side.)
I seem to remember a friend's parent's car having one of these when I was a kid, sometime in the 80s / 90s. This was in Nova Scotia, not a very sunny part of the world so they weren't common here, although cars do get hot in the summer if left in the sun. I think the family or the car had moved here, perhaps from the US, since I think the "need help" message on one side involved "highway patrol". That's not a term we use here in Canada.
I also vaguely remember my friend telling me that his mom once left the "call highway patrol" side facing outward by accident. But I forget what happened next. Presumably someone called them and they were waiting by her parked car, otherwise it wouldn't have been a story worth telling your friends.
Surprisingly here in Iowa, despite it getting up to mid 90s to low 100s almost every summer (like mid 30s to 40C), and loads of parking in full sun so it would get to like 150F (65C) in the car, and plenty of cars made in the 1980s with no air conditioning, I don't recall seeing all that many sun visors ("Call the Police" or otherwise.) I saw a few but not too many. Often in classic cars, to avoid the sun and heat damage to the interior.
As user71659 says, many if not all cars now have glass that cuts down on the heat some, it's for gas mileage reasons, the air conditioning draws puts less load on the engine (or draws less power on a hybrid or electric vehicle) the less cooling it has to do.
I will say, I think the biggest reasons sun visors may be less common now...
Almost all cars now have air conditioning (unless it's broken.) Having the car be even 5 or 10 degrees cooler was a big deal if you were just having to crank down the windows and try to cool off the car with 90 degree outdoor air. With A/C, it's saving like 10 seconds to a minute off your cooldown time instead.
Perhaps vehicle size. Real small car with a small glovebox, it may be inconvenient to store. On the other end of things, if you have some giant Suburban or whatever, how much effect does covering the windshield have when there's 100s of square feet of vehicle behind it soaking up sun? That said these vehicles also tend to have more heavily tinted windows.
Like the other answers show, these were common, inexpensive covers used in hot and sunny locations in the 80's and 90's.
Their use has declined due to modern cars using solar glass that blocks solar radiation. This became universal in part due to US Government CAFE regulations giving cars a fuel mileage credit for having it. Additionally, remote start became common, allowing cars to be pre-conditioned.
Rental cars? No, never saw one in a rental. Drivers wouldn't care about protecting the interior of a rental, and rental companies wouldn't want the hassle of stocking and maintaining them.
Would somebody call police if they saw one on a parked car? No. It was easy to put them the wrong side out. I recall seeing them fairly regularly and we never did anything.
The proper way of summoning help would be to stand outside your broken-down vehicle and wave the police side to oncoming vehicles. I recall one having printed instructions to tie it to to your car's radio antenna.
The sun shades are common in the southern states where it gets in the 90s and up into 100s. The shades are put up in the windshield when you park and you go into work or into the grocery store.
The message of "need help call 911" is when your car breaks down or you run out of fuel. It may have been way more popular back in the days before cell phones but it's still relevant today. Cell service doesn't reach everywhere. If your out in the woods or up in the mountains and especially out in the Everglades in Florida like the character in this movie was but he almost guaranteed got it for the sun visor function to stay cooler sitting in the car for hours waiting for the right time to execute his plan. The Everglades are a swamp and it's difficult to install a cell tower and/or it's so sparsely populated that it's not cost effective for the cell companies to install one of their cell towers out there. So the visors are not only for the days before cell phones they are still used today in the event that the car breaks down in an area where there is no cell towers built anywhere close and the message can be seen from the air if a small plane flying low doing search and rescue. Also planes are quicker to get up into the wilderness areas where someone might have broken down with no cell service.
Something related to this, but possibly more common at the current time, is a tire cover used to cover the spare fastened to the back of some vehicles (mostly Jeep and Jeep-style vehicles).
Some of them have "No Problem" and "Problem" with whichever is at the top is right-side up and the one at the bottom is upside down.
Assumedly these could be used to indicate a vehicle on the side of the road is having some sort of trouble rather than just being left there while the occupants are off hiking.
The reversible shade could be used in the same manner, marking a vehicle as one in need, rather than one just parked somewhere.
