I've wondered for awhile about all the Northern California Rex chips. The ones below all come from clubs within 100 miles of San Francisco. Your Vallejo Rex chips are also in the greater San Francisco Bay Area. I guess it could be coincidence that the most common man's name on cardrooms in the period was Rex rather than John or Bob or Bill, but I think it's more likely there was some sort of connection. Maybe involving the nice folks that ran the SS Rex off Long Beach? Just speculation, but an interesting possible area for research.