Use double sided carpet tape. Apply the decal to the tape, cut around the decal, remove the backing tape and apply to bike. Make sure you clean the area to be applied with something like CD/DVD cleaning fluid first. Did this recently with a NOS Parkpre PFR chain stay protector, kept it for 8 years on it's backing paper waiting for the day I would finish restoring the bike. Applied it to the frame and to my horror it refused to stick. Used the above method with very pleasing results.