Peter:
What are "printed transfers"? Is this something you print on laser printer and then "scratch" onto the surface? Would you mind sharing the product name?
If this works like Lettra Set ie not a piece of printed tape label, you can add durability to it by spraying it with a coat or two of matte finish photo graphic lacquer. (available at any camera/photography store).
Use a very light spray with multiple passes only after previous is completely dry otherwise solvents can disfigure the lettering.
Derek