Brothers Chemical Vinyl-Off Vinyl Graphic and Decal Remover | Professional Use | for Vehicles, Glass, and Signs | Softens Film for Easier Removal Without Damage | Safe on OEM Paint (32oz)

Vinyl-off. You spray it on the vinyl, let it sit (ignore the instructions, let it sit longer), it will penetrate the vinyl and "reactivate" the glue underneath. Should be able to peel it after that. It's a little pricey but a quart is enough for us to strip entire box trucks with. AMAZON LINK