About twenty years ago there was a (official) street sign near here that said "EVOLVE" and had a little circular symbol similar to the Recycle icon. Good advice I suppose, but I'll be damned if I could ever figure out how it applied to traffic in the area.
I also like the signs in Yosemite Nat'l Park that say things like "Stay on the trail or YOU WILL DIE" along with stick figures shown falling off of cliffs to their stick figure deaths.
I have a comic that I have saved for years. There is a cow as a hairdresser, doing a dog's hair. They both have thought bubbles. The cow is saying, "Bitch", and the dog is saying, "Cow".