I actually tried blasting them with a heat gun, seemed to make it worse. they got kind of weak and bubbly. I"m letting them sit overnight before I try and peel the backing off. if still no good I might try some spray adhesive on them
Heat gun might be too much. I used a hair dryer, with the backing off, to carefully warm the decal and smooth it out. It looks like part of the visor now.
This was a few years ago. Assuming that the decal product is still the same.