I have found one of the best adhesive removers is olive oil. It doesn't have any harsh chemicals and so it's safe for just about any surface. I used it to get the sticker residue off my new bike and numerous other things I wasn't sure how safe it would be apply chemical things. Just put a little olive oil on a paper towel and rub on the adhesive. It comes right off - a trick my mom taught me a long time ago!