Green’s Dictionary of Slang

heavy boots favoured first by working men, then by skinheads and latterly by fashionable teenagers.

1982		P. Redmond Tucker and Co 25: There, just sticking out, was the scuffed toe-cap of a pair of DM’s.
1999		N. Cohn Yes We Have No 351: His purple DMs are splitting along the uppers.
2000		Guardian G2 6 June 2: Everyone turned up in their steel-capped DMs.
2004		(con. 1960s-70s) T. Taylor Top Fellas 111/1: They were more inclined to wear D.M’s.