Green’s Dictionary of Slang

1. (US Und.) a thief who operates alone; also attrib.

1927		Clark & Eubank Lockstep and Corridor 174: Lone hand — a thief who works by himself.
1932		Collier’s 3 Dec. 9: Dancing Dan is one of the best lone-hand git-’em-up guys in the world [HDAS].

2. (N.Z. prison) the solitary confinement or punishment cell.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 110/1: lone hand n. the solitary confinement punishment cell.