Green’s Dictionary of Slang

a joking, slightly offensive ref. to a police officer; in 19C also army officer.

1831		Navy at Home I 196: Getting two or three buckets quietly full of salt water; and coming slyly on the nest of sleeping ‘ossifers’ suddenly discharge the contents all over them.
1845		Bell’s Life in Sydney 11 Jan. 1/6: I think a millishy ossifer [...] is just as good as a nigger.
1848		J.R. Lowell Biglow Papers (1880) 21: Our ossifers aint wut they wuz afore they left the Bay-state.
1850		‘Epistle from Joe Muggins’s Dog’ in Era (London) 16 June 5/3: I didn’t know that [...] her was an ossifer in her majesty’s sarvice.
1865		A.J.H. Duganne Camps and Prisons 77: We done heerd one Linkum ossifer readin’ it out.
1865		Melbourne Punch 26 Jan. 33/1: In slang, officer is ossifer.
1897		Kipling Complete Stalky & Co. (1987) 62: But now, he has insulted Number Five [...] in the presence of these — these ossifers of the Ninety-third, wot look like hairdressers.
1908		Sun. Times (Perth) 26 Apr. 1/1: His life was saved by a feather-bed hossifer who always carries a flask.
1909		J. Ware Passing Eng. of the Victorian Era 186/1: Occifer (Colloquial imbecile, 19 cent.). Officer.
1957		H. Ellison ‘Look Me in the Eye, Boy!’ in Deadly Streets (1983) 159: You mean I ain’t even gonna get a trial, Ossifer?
1972		B. Rodgers Queens’ Vernacular 126: the police [...] ossifer (since WW I).
1984		(con. WW2) T. Jones Heart of Oak [ebook] As QX division, our first job was to scrub the quarterdeck which was the ‘ossifer’s turf’.
1987		(con. 1967) Bunch & Cole Reckoning for Kings (1989) 6: You’re supposed to be back at the Ossifers’ Club.
1989		Eble Campus Sl. Mar. 6: osifer – a policeman.
1991		Eble Campus Sl. Mar. 7: occifer – policeman.
1995		R. Campbell Wizard of La-La Land (1999) 96: Yo heard of entrapment? You heard of un-der cov-er police os-si-fer?