Green’s Dictionary of Slang

C-jam n.

also C-jame
[C n.3 (1) + jam n.5 (1)]

(drugs) cocaine.

[US]Duke Ellington [song title] C-Jam Blues.
[US] ‘Sl. of Watts’ in Current Sl. III:2 15: C-jame, Cocaine.
[US]Spears Sl. and Jargon of Drugs and Drink 109: C-jam noun cocaine.