Hi Steve;
I once found a necklace with all these chips at a flea market. Paid a cool $7 for the whole thing. It had a couple of the chips you had pictured and a chip almost like that one and, one a little larger and gold inlay and the number 40 which you could make out a fancy MC on them. Also was included were 5 or 6 serial numbered SDM chips beautiful colors. That told me that these were from the Monte Carlo.

I noticed that your chip is drilled in the same place as my 20 chip, I am guessing at one time someone decided to make necklaces out of old Monte Carlo chips. I threw away the necklace and kept the chips.

Best Regards
Michael Petty