Although two current UD definitons have it as 'punk' origin and used in the 70s, it was widely used as early as the 50s in Brooklyn and other areas of NYC and possibly beyond.
Sometimes it accompanied tags of gangs, but mostly it was used as a postscript with tags of gang members or wannabe gang members.
It was also frequently preceeded (separated by a space) by D.T.K. = Down To Kill
and followed less often by TTH = To The Heart
The acronym might be combined with their community or other name, as Kings LAMF and was often written with marker pen inside subway cars in New York City.
The term stood for "Like A Mother Fucker" and was also used as the title, in that context, albums by Folk-Rock Duo Bunky and Jake in 1969, L.A.M.F. and Johnny Thunders and the Heartbreakers in 1977, L.A.M.F.
In the present, some bands and individuals use the term LAMF to evoke connotations of said Johnny Thunders and the Heartbreakers album and the musical milieu that gave birth to it.
LAMF is also the name of the Burden Brothers Street Team.
Vans Skate Footwear has also released Jim Greco's pro model shoe, called the LAMF. Van's has also come out with the LAMF 2's.
Julian Cope and collaborators released an album by LAMF called Ambient Metal in 2001.
Japanese professional wrestler Yoshiaki Yago has the letters "LAMF" emblazoned on the back of his trunks.
Shannon Leto, of the band 30 Seconds to Mars, can often be seen wearing a shirt with the acronym LAMF written across the front in Pink lettering.