No more bumperstickers, or - park where you can set-up quality video cameras so the vandals may be identified and law enforcement will subsequently do nothing about it.
BINGO. That is exactly what will happen. Nothing.
They might if you put NOBAMA stickers on their cars and those of their relatives.
I don't say it's easy or convenient, but you have to get a lot of NOBAMA stickers and slap them onto a lot of bumpers.
Oh, and windows too.