Green’s Dictionary of Slang

stir adj.

[stir n.1 ]

pertaining to prison.

[US]R. Chandler ‘Goldfish’ in Red Wind (1946) 168: At last he said in his lipless ‘stir’ voice.
[Aus]Smith’s Wkly (Sydney) 26 Feb. 3/5: The assaulted ‘stir’ socialites enlisted the aid of two notorious desperadoes.
[UK]J. Curtis They Drive by Night 19: It felt a bit different from stir-clobber.
[US]P. Rabe My Lovely Executioner (2006) 23: Then I heard Rand’s ‘stir’ voice [...] the sound we learned to make without using our lips.