Use a blow drier, heat the sticker and peel it off. If the paper part is all mushy and won't peel off by pulling, use a razor blade to scrape it off after heating it up. If you have residual sticky shit on the window, any decent soap will remove it (especially if warm). You shouldn't have to spend a dime on any fancy chemical remover.
Defroster lines are on the inside, so using a razor isn't an issue unless the stickers are on the inside ....nothing like pointing out the obvious
