Thak you all again for all of your input. As far as liability goes, ehh, we'll deal with that.
Liquid flypaper, REALLY sticky stuff, Black Axel grease, the kind that stains your hands if you get it on you, and some Ink (Bush blue) from a pen. It is on both sides of the top of the sign.
MMUUUAAAAHHHHHHHHHH he he he
The only down side is that he will probably wipe his hands on my white car that sets next to the sign.
I am also keeping an eye on the sign tonight, but don't expect to catch him. It will be fun if I do though.