Stickers can be safely and cleanly removed from car windows and bumpers using a razor blade scraper and denature alcohol as a solvent. Here's how:
Actually, it's quite simple to remove stickers from a car's glass, chrome bumpers, or painted surfaces. The first step is to go to the hardware store or a paint store and buy two items: a razor blade scraper with a straight edge and a handle to safely hold it, and a small container of denatured alcohol. These items and perhaps a clean rag or two are all that you need.
Stickers on glass are the easiest to remove. The razor blade scraper will take them right off, and will not scratch the surface of the harder glass. There will probably still be some residue after all traces of the sticker are removed, and that is where the denatured alcohol comes in. Dab some on a rag and use it to scrub away the glue residue. That's all there is to removing stickers from any kind of glass.
Getting old stickers off of a painted surface is another matter all together. The razor blade scraper will work, but you must be very careful or you will take off a layer of paint as well. The key is to hold the scraper at a low angle and work on small areas of the sticker at a time, starting with the corners. If you can slide the blade carefully between what is left of the sticker and the painted surface, you might be able to peel at least part of it up. Relatively new stickers come off with ease and can sometimes be peeled up in one piece. The older the sticker, the harder it will be to remove. You might have to remove it in tiny bits, alternately scraping with the razor blade and scrubbing with denatured alcohol to loosen the glue. Denatured alcohol is an excellent all-around solvent that is mild enough not to damage paint. Stronger solvents such as acetone would work faster, and are okay on glass, but might dull the paint finish permanently. Some solvents might even remove paint and ruin the finish. So no matter how resistant the sticker and residue are to removal, don't be tempted to try anything but denatured alcohol.
Once all stickers and their residue have been removed, wash the car with soap and water. The alcohol should have evaporated by now anyway, but it doesn't hurt to wash it off. Given the difficulty of removing really old stickers from a painted surface, you might want to limit future stickers to the glass or replace them after a year or so before they start to deteriorate.
