I’m a big fan of Yubikeys. They’re nice and easy to use and add an extra layer of security. We use them at Code Enigma too, which means that I have a bunch of them for various tasks. The problem then becomes identifying which Yubikey is which.
I could have just used stickers, but as I carry my Yubikeys on my keychain, I didn’t think stickers would last very well. A quick enquiry on the Yubikey forum confirmed that the keys are made from ABS. I’ve worked with ABS before and it can be easily solvent welded using acetone.
A cheap source of some ABS in various colours is the selection packs of filler rods used for heat welding repairs to plastic car body parts. I found a pack on eBay.
Using some acetone, I solvent welded the ABS strips onto the edge of my Yubikeys, then trimmed the strips down to size, before sanding them down flush.
Now, I can quickly identify which Yubikey is which, and they still stack nicely together on my keychain.