Responding to one of my New Year's Eve posts, Aaron Haspel of God of the Machine mentions another amusingly ambiguous sign, which reads:

No Soliciting
Violators Will
Be Punished

That reminds me of a sign that was once quite famous, at least in the academic world. Near the University of Chicago there is (or was) a fried chicken place -- very tasty, as I recall -- part of a small local chain called, I think, Harold's. It was take-out only, so there were no tables or chairs, just an order window and a fairly large room where customers could get out of the weather while they waited for their chicken. The owner (presumably Harold himself) wanted to keep the room clean and uncluttered, so there was a sign that read:

This was a source of amusement to Hyde Park residents until William Safire mentioned it in his language column in the New York Times. Two days later, it disappeared from the store, though I've heard that it reappeared at one of the other branches further from the university. As one of my friends said at the time (hi, Malcolm!), it's interesting to consider how many degrees of separation there were between the owner and whoever read the Safire column. The fact that it took two days suggests that there were at least one or two intermediaries.