Green’s Dictionary of Slang

(N.Z. prison) the hitting of an inmate’s cell bars to chck that thewy have not been sawn hrough as a preliminary to escaping.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 95/2: jingle bells n. a procedure whereby officers hit the bars of inmates’ cells with lengths of wood or metal to ensure that inmates have not tried to cut through the bars in an attempt to escape.