What visual cues distinguish the different floors on The Big Bang Theory?

Question

I have recently begun watching The Big Bang Theory. Mostly passively, this is my wife's new show. For this reason I have noticed some things, but haven't watched closely enough to notice small differences.

I wonder about the fact that each of the floors look the same as they walk upstairs. Researching further, I see that the three floors (including the one they live on) with two staircases and a warning-taped elevator are all actually the same set (see item #2 in this list).

This site does reference the fact that they make small changes to distinguish each of these three floors. Does anyone know what these differences are? Are they listed somewhere on another site?

Answer 1

Small elements are changed such as plants and the door numbers

Noted here: How does ‘The Big Bang Theory’ staircase work?

• However, in reality, there is only one hallway-staircase set on Stage 25 on the Warner Brothers lot (a separate set is available for the lobby, which connects to the stairs). When scenes involving multiple floors are filmed, the same set is redressed to appear to be different floors — the production design and set dressing teams change out the apartment number plaques and add or remove items ranging from water jugs, potted plants, decals and bicycles to make it appear that each part of the scene is on a different floor.
• The yellow tape and “out of order” signs on the broken elevator are also changed for each “floor.”
• The doors are mostly kept closed or shot in a way that hides the fact that they actually lead to the fourth floor apartment sets.
• If you look closely, you can see that, on each floor, the scuffs on the walls and baseboards are the same on each “floor”.

This GIF shows each floor and the differences, from the Buzzfeed article: 10 Fun Facts About The Big Bang Theory.