I have over 500 ivories and agree with Rich. Here's a story about unidentified ivories.

I found a wooden shipping crate of ivories sent to the then owner of a casino in Saratoga, NY, 1859,...no I.D. on the chips nor have I ever seen i.d.'s on other chips except as described by Rich. I offered a set to a museum in Saratoga that featured some items connected to illegal gaming; the curator declined saying that there was nothing on the chips (horseheads) that could be linked to a Saratoga or Balston Spa casino. (as I no longer had the shipping crate I couldn't provide the information.)