There’s not much room on an AT26 / TF26 can for a readable label, unless one owns a metal-marking laser, but a simple bar code should let me identify each one:
The empty “0” slot down at the bottom will hold the crash-test dummy resonator I’ve been using to get the tester working.
The red-and-blue stripes from plain old fine-point Sharpie pens will rub off under duress, which I hope to avoid. After finishing up, I’m still not sure blue makes a better zero than red; you can make a convincing argument either way:
The bag allegedly contained 25 resonators, although I’m willing to agree the last one escaped into the clutter on or under the Electronics Workbench.
The Smell of Molten Projects in the Morning 
I discovered recently that Brother makes heatshrink tubing cartridges that fit their ptouch labelmakers. It is intended only for the $$$ industrial industrial ones but works just fine in the dirt cheap yard sale variety and comes down to quite small sizes. Maybe easier than this and certainly more durable :)
Amazon has it down to 5.8 mm, which Brother claims will work on 1.7 mm OD things:
HSE211
I like the idea, but given the usual wastage between labels, 1.5 meters might barely cover those two dozen resonators. Ouch!
The nicer labelmakers can print a whole string of serialized labels in one go with no waste, but the cheaper ones might not. (I recently blew way too much money on the PTE500 and it’s wonderful but crazy overpriced)
The PT-1090 sits on the dim end of their offerings, without automagic serial numbers; I must enter all the numbers with an appropriate number of spaces between them, buzz out one huge “label”, and wield the scissors. Getting neat results requires careful attention to detail and, for me, seems hit-and-miss.