I was recently watching some old Tom and Jerry episodes (40s-50s) and noticed the end of the episodes have a star shape symbol in the top right for only a few frames. I couldn't find a term for what it was, I'm thinking it may be an visual artifact or a stamp of some sort. I haven't checked but I'm guessing these probably appear on similar cartoons like Looney Toons as well.
What is the cause/purpose of it?
Here's an example from a few episodes: