To remove a bumper sticker from a vehicle, spray on a little spray lubrication, like WD-40. Then work a plastic spatula (or paint scraper) under the corners until you can get as much of it up as you can. Don’t use a razor blade, as it will scratch up the paint.

You might also try using a hair dryer to heat and loosen the sticker.

When you have the sticker off, use a plastic scrubbie and dish soap to get leftover adhesive. Follow that with rubbing alcohol.