Green’s Dictionary of Slang

clink n.3

[? fig. use of clink n.1 (1), so many blacks being imprisoned, or f. clinker, a grey-black ash that remains after a fire]

(US black) a black man.

[US] ‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
[US]Wentworth & Flexner DAS.