...but apparently not in Florida, where you need to use a billboard:
I saw this on a recent trip to Florida, and after some digging, found a whole state-sponsored website devoted to this. Is this really a problem? Reminds me of that scene in The Jerk when Steve Martin is asked to help stop the spread of cat juggling in Mexico. Come to think of it, maybe this is another Southern thing that I'll just never get, right up there with NASCAR, grits, and anti-intellectualism.