Depending on the specific type of vinyl decal, application tape (or transfer tape) may be used to aid in applying the decal to the mounting surface. This is more typical with contour-cut, pre-spaced vinyl decals (eg., cut lettering). These days, if it's a large rectangular-shaped piece, we tend to not use application tape, but instead burnish right on the printed surface of the decal using a felt-lined squeegee. Hope this helps!