Just noticed this for the first time today
I went into the city for some business and stopped at a local chain gas station for a coffee.
As I was walking out the door I noticed that on each side of the door there were rulers on the door frame. I think they started at 4 foot but did not notice the lower limit as I was looking at the higher limit 7 ft.
The markings must be for when the store gets robbed so the clerk can give the height of the robber easier?