What’s a “Rummy Name”?

From People v. Morris (Cal. Ct. App. Oct. 5),

Either codefendant Carline Balbuena, whose self-chosen rummy name was “Queen of the Damned,” or defendant James Morris, aka “Ultimate Evil,” delivered the fatal blows to Balbuena‟s three-year-old son, Keith Carl Balbuena (KC).

What’s a “rummy name”? My searches couldn’t find a meaning for the phrase, other than in the British sense of “rummy” (i.e., peculiar, probably in an unfortunate way). Or does this relate to some unknown to me practice of people who play the card game “rummy”?