Green’s Dictionary of Slang

hamma n.

also hammer
[? they ‘knock one on the head’; but note hammer n.1 (5)]

(US black) a very attractive black woman, occas. extended to men.

[US]Current Sl. IV:2 7: Hammer, n. A girl — Junior high school males. Negro. [Ibid.] V:2 8: Hammer, n. A pretty girl.
[US]H.E. Roberts Third Ear n.p.: hammer n. 1. a female. 2. a sexy female. 3. a shapely female.
[US]W. Safire What’s The Good Word? 80: He will take out his hamma, or sleek lady, sometimes used derogatorily as the opposite of foxy lady, who may become his main squeeze.
[US]Eble Campus Sl. Mar.