Green’s Dictionary of Slang

(US prison) a black person.

1981		Maledicta V:1+2 (Summer + Winter) 267: Other terms commonly heard in prison life are [...] and reggin for a black person. The latter does not carry the same ugly meaning as it does when spelled in reverse. It is more of a non-controversial term used by both races.
2000		Ebonics Primer at www.dolemite.com 🌐 reggin Definition: A individual of African-American descent. Example: Man reggin you better back the fuck up or you gonna find yo azz 6 feet unda’, bitch!