This was her apartment, I gathered, and he was living here. That was his MO. He would leech onto some girl and eventually move into her home. 2022, Ling Ma, “Oranges”, in Bliss Montage, New York: Farrar, Straus and Giroux, →ISBN:
The Big Man is everywhere. He knows my M.O.!!!! 1981, James Ellroy, Brown's Requiem, page 207:
(abbreviation, alt-of, countable, initialism, uncountable) Initialism of money order.