I did this with the card suits(spade/diamond/heart/club) on my Surly. Traced them onto the backing and then just cut them out with the small scissors on my SAK. Should be easy to do with an X-acto.
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C'dale BBU('05 and '09)/Super Six/Hooligan8and 3,Kona Dew Deluxe,Novara Buzz/Safari,Surly Big Dummy,Marin Pt Reyes,Giant Defy 1,Schwinn DBX SuperSport,Brompton S6L/S2E-X/M6L-X/S12 T Line