Though some are traced to swanky San Francisco hotel ballroom gambling operations by French syndicates, the use of two or three numbers wasn't common in Europe back then and maybe an American request for whatever reason(s).

So far, nothing (or possibly very little) had a location name on the MOP's in California and down to Mexico... and only monograms of the operators since operations moved around depending on entertainment and what the rent of the room was (up to $6,000 a month for some rooms). Some notes seem to indicate that one location (hotel) had more than one operation going on which, we know wasn't uncommon in some French locations noted on ChipGuide.

No idea where these are from.