As in smaraṇa स्मरण - Remembrance
摩字門，入諸法摩字不可得故
Kumarajiva
入颯磨字門，悟一切法可憶念性不可得故
Xuanzang
SMA because remembrance (smaraṇa)
Conze
SMA the syllable sma [means] all mental phenomena are openings because of the non-recognition of recollection (smaraṇa)
Jayarava