As a rule, so can call the client in American casinos. Outside the United States, this nickname is much rarer.
George is a casino customer who does not skimp on tips.
Often to the nickname "George" add prefixes "Super", "Mega", "Hyper", king Kong", meaning that the client is very generous.
This is usually referred to as players for the eyes. If you find out that you are nicknamed "George", think about whether you spend too much money, want to thank the dealers. This tactic can ruin you, because in most gambling mathematical advantage and so on the side of the institution.