Take on the "proper OR attire required" sign

The last thing I remember before they cut my manhood last week was a sign on the door of the emergency room which stated

NO ADMITTANCE
Restricted Area
Proper OR attire Required

What I'm confused at to this day is what the OR stands for in this sentence. I realize that I am an ESL student, but what the hell does that mean?!? "Proper attire required" would make sense as you wouldn't want a cowboy strolling in with assless chaps but the OR really confused me. Do you either have to be proper OR required to be dressed which I guess is sort of the same thing.

Really, I'm not sure.