As Mike said, 2-MF-x stands for VMF-2 (Marine Fighting Squadron 2). This is the
current VMA-211 "Wake Island Avengers". Marine squadron numbers were assigned
sequentially, not by base location.

Until 1944, the only Marine squadrons assigned to carriers were VS-14M and
VS-15M (pre-1937 designation system). These scouting squadrons operated from
Saratoga (VS-14M) and Lexington (VS-15M) from 1931 to 1934.