Just thought I'd share the labeling system I worked out for my USS machine. Since you can't see the bottle caps, I went out and bought a set of magnets from Michaels (link below), which worked out perfect for mounting the bottle caps. I used hot glue to attach one magnet to the turn-handle, and the depth of the caps allows it to sit perfectly.
http://www.michaels.com/art/online/displayProductPage?productNum=gc0460The pack comes with a whole bunch of magnets, so I put the rest on the inside of the coin door and now I have a whole collection of caps for when the machine is stocked.