I also did a Google search, and by coincidence came up with this funny story by a Kerry supporter who unintentionally removed his bumper sticker:
"I used duct tape to cover up my Kerry bumper sticker because I was doing volunteer work for a non-partisan group on election day. When I stripped off the duct tape this morning, it took the bumper sticker with it, leaving just a couple of very small spots of adhesive which I scraped off with my fingernail.
"You should cover the bumper sticker completely, folding over the ends so they don't stick. Then slowly pull it off, starting at either end. It may help if you leave the duct tape on for a while. I had it on for 24 hours."