I had a friend get his car keyed and his Bush/Cheney sticker half torn off.
I think your sign being stolen isn't right, but you don't have a problem, as far as I can see, just a "WTF" moment that will pass tomorrow.
How much did you pay for your sign? If it's ~$500 (the amount of damage to his car) then I'll get behind you.
This kind of crap is happening all over, and by both parties. It IS terrible, but NO ONE seems to be shocked, I only hear dismay that it's happening. I'm betting it's due to terrible parenting, but that's just me.
If you're one of the asses doing this (not you, Cooter, this is a generalization) to people's property, I hope they catch you and beat the snot out of you....I don't have a pistol, but if I caught someone stealing my sign, I'd rubber-chicken-whip you.