"Kyle Boatright" wrote

Mineral spirits works well, and won't hurt the paint. It is the primary
ingredient in most of the "tar removal" products sold for cleaning
automobiles.

Some stick-on removers contain mostly naphtha. (commonly know as cigarette
lighter fluid) Try that.

If the sticker has a face that will not peel off, then the solvent can't get
to the glue. Try taping a solvent soaked paper towel over the sticker, and
a piece of plastic on top of that, and let it stew over night. If you can
prick the decal with something like an exact knife, that will also help the
solvent get down to the glue.
--
Jim in NC