As a special favor for game designers, I also sell special PennyGems for prototyping. It's basically the usual miracle of modern science polyurethane dome over a blank label. For short term use, a buyer can draw a carrot, taxi, space station, or earwig on the token with a transparency marker. The ink will rinse right off.
For a more durable graphic, use permanent marker. Note, however, that "more durable" is definitely not "forever." "Permanent" marker can be rubbed right off a PennyGem if somebody presses firmly, or you can wash it off with isopropyl alcohol. A small percentage of such markers leave behind a faint yellow stain, so you might want to test a new marker first.
Blank White Regular
Most bank for your buck, and tends to be the more useful size. One sheet provides twenty tokens.
Blank White Jumbo
Sometimes you just need more room to write or draw. Thus, the availability of quarter-sized Jumbo gems.
If that's still not good enough, we even offer self-adhesive transparent domes. You can print out a fancy label to make your own customized tokens and still enjoy the quality feeling of PennyGems. There are a couple of caveats, however.
First and foremost, if your label doesn't have an industrial grade adhesive, you should use labels 3/4" or smaller, so that the dome has a clear edge to adhere to. The other is that the substrate is a fresh copper-plated disk, so if you leave room for the label to touch down on the edge of the coin, you'll have to live with a fairly broad copper margin.
Also, if you stick your label on the disk, and the dome on the label, and a few days or weeks later the dome&label pop free, the merest hint of superglue should lock everything back together even more permanently than it was before.