Confusing Recursive Sign
I'm fairly certain that there's an explanation for this self-referential and recursive sign, but I don't care. I don't want to know it. "Watch out for the sign! Don't hit your head on the sign!", the sign depicts. That's like getting a telephone call telling you to answer the phone.
In one of my Computer Science classes today there was a sign on the door that said "Don't Block This Door". Leaning against the door was a stack of chairs, a table and an overhead projector.
Link (via Boing Boing)