All printed decals should be lacquered over for a professional and permanent finish. Failure to apply the lacquer can result in premature wear to the print. Comprehensive instructions are available here on my web site, details of which will accompany the decals.
I would advise against using these decals on a frame that has been powder coated unless this has been applied by a professional company who understand cycle frames and not the type who simply do 'iron gates'. Powder coating is without doubt a very tough finish, but can be difficult to adhere to, especially matt finishes. Best to apply to a stove enamelled frame, by an experienced frame sprayer.