Green’s Dictionary of Slang

crown n.2

[‘a crown was worn on an insignia of rank on the lapel. This practice is now obsolete but the term is still used to denote a prison officer in authority’, Tupper & Wortley, Australian Prison Slang Glossary (1990)]

(Aus. prison) the Principal Officer.

[Aus]Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Crown. Principal prison officer.