Ok, there's nothing funny about sexual harassment. Ask Ben Roethlisberger (though he was accused of the more serious sexual assault).
That being said, there are serious ways to get the point across. And then there's this, posted by Natuba member nailbiter2:
I guess some people really misconstrue it as a compliment. The decaying rose really does it for me. But again, the act isn't funny... this sign is. Besides, nailbiter2 lol'd first!