It's very naughty to tell your kids stuff that's, well, just made up, just because it's so funny that they'll believe anything. I was so noble about the whole Santa Claus thing, not wanting to lie to my kids about it.
But then the other day Leo asked me about this sign. He can recognize the letter P, and he knows what the red circle with a slash means on a sign, so naturally he was wondering precisely what it means you're not allowed to do.
"It's obvious," said I. "You're not allowed to pee here."
Obviously, he believed me. (It probably helped that he's from France, where "no peeing" zones are the exception, see my scrapbooking post.)
Don't worry though! Leo's Daddy later told him what the sign really means: "no parking."
And Leo didn't believe him...