Green’s Dictionary of Slang

1. (US prison) an ice-pick.

1994

P. Baker Blood Posse 310: Hew [...] handed me an ice pick [...] ‘That’s what they call a dang wang or jammer.’.

2. the penis.

1991		Daddy Woody ‘Ramma Jamma’ 🎵 The girls want the jammer / Hard and warm.
2011		J.J. Connolly Viva La Madness 34: Sonny [...] had the jammer up a ten-dollar hooker.