Why not just use a black Sharpie, fine point marking pen? Mark the tube on the glass itself, somewhere that you won't be likely rub off(very top/bottom). ( http://www.staplesindustrial.com/shipping-supplies/markers?cid=PS:MS:SBD:SI:B:23:20529:sharpie_markers ) I mark the order of my octets of main amp power tubes this way(bottom of envelope), just so I'm certain of replacing them in the same positions, in the amps, anytime they're removed.
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A small label will not comprimise the Tube . Heat from the Tube will cause the adhesive to stick to the glass envelope , but can easily be cleaned .
Most vintage European Tubes have etched Codes on the bottom of the glass . The top line is the Tube Type Identifier . The second line contains the Factory Identifier along with the Date Codes . A web search will provde the needed site for this info .
A magnifying glass may be needed to read these series of Letters and Numbers . Being etched into the glass means it can't be rubbed off .
For labeling tubes I just grab a sharpie like what Rodman states and write carefully on the glass itself where I won't touch them frequently. For 6SN7 type tubes I would put a small label on the base.
Check out the Brent Jessee videos on how to identify various rare 12AX7 and 12AU7 type tubes.
I prefered to put removable labels on the back of the gear that the tubes were in that corresponded to the tube positions, but anything that works is fine.
Realize that, if you are buying tubes with no labels, the boxes alone do not speak to the authenticity of those tubes. A bit of research on the engraved codes and the plate and getter structures of the tubes that you purchase can be a very good thing. An investment in a tube tester is not a bad idea either. Unfortunately, everyting on the net is not what it seems.