I've used the Datak dry-transfer labels (position, rub, clear spray, done) for years and found them to be very effective. Packs of letters and numbers are available along with specific "name" packs for amateur radio, audio, test equipment, etc. They should be available from the "big" industial suppliers, but places like Ocean State Electronics,
http://www.oselectronics.com/ose_p52.htm also carry a big selection. Not very expensive.
It you have an ink jet or laser printer, you can go to any office supply store and buy packs of clear labels that are used as mailing labels. You can generate whatever words you want, in whatever font you want, in whatever color you want, and print them on these labels. Cut away the unused part of the clear label. The labels are mounted on a waxed type paper for easy removal. Generally a clear spray coat or two over the labeling surface area can easily mask label end material.
