Green’s Dictionary of Slang

(Aus.) a police car or van; a ‘Black Maria’.

1924		G.H. Lawson Dict. of Aus. Words And Terms 🌐 TRAWLER — Police patrol van.
1935		A.J. Pollock Und. Speaks.
1938		H.B. Raine Lash End 95: ‘Is the trawler here?’ .. ‘Coming round the corner now, sir’... He ran downstairs to tell the ‘Black Maria’ driver to open the door leading to the female half of the big vehicle [AND].
1945		Baker Aus. Lang.
1955		Bulletin 9 Feb. 25: He can tell ... whether it is a ‘trawler’ (black-maria), a P.D. car, a carload of scientific experts.
1977		D. Foster Escape to Reality 91: A trawler came cruising by [AND].