Car window bar code stickers are usually affixed to the outside of the window using a strong adhesive that will cause the sticker to tear when it is removed from the window. This is necessary to prevent the bar code from being stolen and then used illegally. Unfortunately, this also has the effect of making the bar code difficult to remove when necessary, for legitimate purposes.
Warm the sticker by leaving your car out in the direct sunlight on a hot, sunny day, or use a blow dryer on it. This will soften the glue, allowing the sticker to be peeled off much easier.
Pour mineral spirits or an ethanol/water solution into a spray bottle and spray the liquid onto the sticker. Saturate the sticker with the liquid, but take care not to get any of the liquid onto the car. Alternatively, saturate a soft cloth with mineral spirits or with "Goo gone" cleaning solution and to use this cloth to wet the sticker and remove any lingering adhesive from the car window.
Wash the entire area you have just sprayed, along with the surrounding area (just in case some of the liquid managed to find its way there) using water and car washing soap. This will prevent any liquid used for the sticker removal from damaging your car's finish.
Peel the sticker from the car window using your fingernails or scrape it off using a plastic squeegee.
