Green’s Dictionary of Slang

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

1970		Current Sl. IV:2 7: Hammer, n. A girl — Junior high school males. Negro. [Ibid.] V:2 8: Hammer, n. A pretty girl.
1971		H.E. Roberts Third Ear n.p.: hammer n. 1. a female. 2. a sexy female. 3. a shapely female.
1982		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.
1984		Eble Campus Sl. Mar.