I've also heard wd-40 worked but have no personal experience using it. I buy my car care products from griots garage and they also sell this: Adhesive Remover, 8 Ounces - Restoration - Car Maintenance - Griot's Garage
Try placing a a piece of sturdy clear packaging tape over the sticker your trying to remove. Them with a fingernail or something else that won't damage your paint get a corner started then use the packaging tape to help to remove it. As mentioned above WD-40 should dissolve the adhesive. The tape will help also if it one of those types of stickers that fragments when being removed to prevent theft and fraud. Posted from my iPhone via the Tapatalk app.
Hairdryer, works clean. i've removed and replaced all four w/ new, one time since initial install in '07