Green’s Dictionary of Slang

(UK black/gang) in prison or moving between prisons.

2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 192/2: on tour n. on a transfer to another prison.
2018-20		T. Thorne (ed.) ‘Drill Slang Glossary’ at Forensic Linguistic Databank 🌐 On tour - serving a prison sentence - moving from prison to prison.