Green’s Dictionary of Slang

(US black) a Buick Riviera.

1972		E. Folb Urban Black Argot 144: Riv a Buick Riviera.
1980		E. Folb Runnin’ Down Some Lines 114: Like you have a Riv, a big, beautiful, expensive car with a console. [Ibid.] 252: Riv, Rivie Abbreviation for Buick Riviera. Rivie hog See Riv.