Honestly, this is not the most spectacular or exciting application I've done this week, but it's just a small thing that made a big difference to someone.
This fellow bought a bass electric guitar, and the case it came in had a bunch of stickers, which he tried to remove with some GoofOff, ruining the finish on the surface of the black plastic case.
My solution was to apply a strip of matte-black high-performance vinyl onto the case, covering the messed-up area, and then adding the lettering (and the bass clef).
(I used the high-performance because the case was not smooth, it had a texture, and high-perf. works well adhering to a rippled/stippled surface)
Result --- one happy bass player, $75 in my pocket, and the lesson learned that simple can be sweet.