Green’s Dictionary of Slang

(Aus.) a policeman.

1886		Eve. News (Sydney) 27 Apr. 7/3: Many have been the ‘coppermen,’ as Joe still delights to call the police, who have carried the scars of conflict inflicted by their dreaded enemy.
1894		Truth (Sydney) 11 Mar. 4/5: At his eleventh hour he suffered nab, / A beastly curious and persistent copman / Would not believe he was a languid shopman.
1897		W.T. Goodge ‘Great Aus. Slanguage’ in Baker Aus. Lang. (1945) 117: A policeman is a johnny / Or a copman or a trap.
1901		Sydney Sportsman (Surry Hills, NSW) 11 Sept. 2/5: Why ain’t they took up, I wonder, / Where’s the copperman in blue?
1906		E. Dyson Fact’ry ’Ands 88: There was er John in ther nex’ room, er copman.
1911		Truth (Sydney) 8 Jan. 12/4: Coppermen ain’t game to move ’em / (As, dear sir, of course they ought).
1955		N. Pulliam I Travelled a Lonely Land (1957) 232/1: copman (copperman, John Hop) – a policeman.