~~~ and part of a monogram, especially in France; the M means Municipal.. and, though a no brainer with the examples seen below which are metallics, the bone, pearl and composition from the same casino may not spell out the house name and just have the monogram which can, and in several cases, not match exactly with what is on any of or all of the other forms the chip is known in... It is also not uncommon for one chip to have two different monograms with the same letters; one on each side even when the casino name is spelled out.

Don't ask me why. I don't know... 🤔