Personally, I don't like BM as an abbreviation.  And "abm" has seemed like a contradiction in terms.  I very much like the idea of Human Milk.   Other milks are mostly named according to their source -- goats milk, rice milk, soy milk.  (The exception is cows' milk, which is seldom identified in general discussion, because when we say "Milk," it''s assumed to be cows' milk, unless otherwise specified.)   As much as I like the sound of mothers' milk, all animal milk comes from those animals' mothers.

 So if we can ever establish a vote, mine is for Human Milk (HM) and Human Milk Substitute (HMS).

 (While I appreciate another lactnut's observation on the acronym for Substitute Infant Nourishment, I feel it would make people feel doubly guilty when for reasons beyond their control they have to give a baby
some preparation other than human milk.   I firmly believe in offending the people I want to offend.  I just don't want to offend those who have no choice in the matter.)

Sincerely, Chanita, San Francisco