Believe it or not, stickers and labels stuck with an adhesive to your window glass can be removed -- and without a trace of glue residue. How? It's not magic; it's isopropyl alcohol.
Soak part of a soft cloth with isopropyl alcohol (also called rubbing alcohol). Apply the cloth to the sticker, and gently rub the area until the sticker begins to lift and the glue dissolves. Lemon juice or a nail polish remover that contains acetone will also work, if that's what you have on hand. For best results, wait a few minutes after applying the adhesive remover before peeling off the label, and just as when you're cleaning window glass, removing adhesive from glass should be done out of direct sunlight.