Remove a bumper sticker using WD-40, a putty knife with the blade wrapped with duct tape and rubbing alcohol.
Spray sticker with WD-40, and work to start peeling it off. Gently scrape with a putty knife with its metal blade wrapped in duct tape. Wipe the sticky remains with a soft, lint-free rag dampened with rubbing alcohol. To finish it off, buff with a polishing compound and a fresh coat of wax.