Green’s Dictionary of Slang

fork n.1

1. [late 17C–18C] a spendthrift, a wastrel.

2. [late 17C–mid-19C; 1940s] (UK Und.; 1940s US) a pickpocket.

3. [early 19C+] (orig. UK; US black) usu. in pl., the fingers, esp. the middle and forefingers.

4. [mid-19C+] usu. in pl., the hands.

5. [late 19C+] the crotch; thus ext. as the penis.

6. [1980s] (Aus.) a jockey.

In phrases

hawk one’s fork (v.)

[1970s+] (Aus.) to work as a prostitute; the ‘fork’ is the juncture of the legs and thus the vagina.