This symbol is redundant in the IPA, and is included for historical reasons. It is only attested as an allophone of /m/ (or some other nasal) before [f] and [v]. (Phonemic /ɱ/ has been claimed for a single language, but that claim is disputed.) Per normal IPA conventions, the sound it indicates should thus be transcribed as ⟨m̪⟩. However, several votes to retire the letter have failed.