Green’s Dictionary of Slang

1. (UK Und.) an experienced criminal.

1812		Vaux Vocab. of the Flash Lang. in McLachlan (1964) 247: judge: a family-man, whose talents and experience have rendered him a complete adept in his profession, and who acts with a systematic prudence on all occasions, is allowed to be, and called by his friends, a fine judge.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1812].

2. (US) used in direct address to a man whose real name is unknown.

1845		in Saint Louis (MO) Reveille in Oehlschlaeger (1990) 226: Yes, Judge, that’s the talk, I believe!
1878–81		W.G. Marshall Through America 239: To be called ‘boss,’ ‘captain,’ [or] ‘judge’ [...] by the people you meet when you are travelling is all very well [HDAS].

3. (S.Afr.) a senior figure in a prison gang, among whose tasks is to authorize the assassination of a fellow prisoner.

1984		Rand D. Mail 23 Aug. n.p.: The SA Prisons service does not recognise or grant any special status to the ‘Generals’ and ‘Judges’ elected by prison gangsters.
1991		J. & W. Branford Dict. S. Afr. Eng. (4th edn).

4. (Aus.) a manual labourer who shirks on the job [such a person is ‘always sitting on a case’].

1991

National Times (Sydney) 25 Jan. 24/2: A lazy wharfie would be known as ‘the Judge’ because he was always sitting on a case, and another ‘the London Fog’ because he would never lift.