It's hard to close the windows after you've left the room

I was in a room at work today that had a sign on the inside of the door saying something like this:

CLOSE WINDOWS

BEFORE LEAVING

THE ROOM

Underlining is the written form of stress on that word (before), and that kind of stress in that position can only make the word contrastive. That is to say, it contrasts before with after and any other word from the appropriate semantic and syntactic class (while, during, etc). It also makes before the focus of the sentence, so that the rest of it seems to be already-known information. The implication is that people have been trying to close the windows after they've left the room, it hasn't worked out well, so now we're being reminded to do it before and not after we leave.