There is a device called a decal eraser that is a wheel you put in a drill or a slow speed air tool. It is made of a eraser type material and is available at auto parts stores that cater to the auto body shop trade. Used by most all the body shops. I used it to remove remove decals and it worked pretty slick. Just be gentle and don't get the surface you are working on hot with too heavy a hand.There will be a shadow where the decals were.