Green’s Dictionary of Slang

latch n.¹

(US) a buckle or breast-pin.

1791		‘Flash Lang.’ in Confessions of Thomas Mount 18: Buckles, latches.
1848		Ladies’ Repository (N.Y.) Oct. VIII:37 316/2: Latch, a breast-pin.
1943		D. Burley N.Y. Amsterdam News 18 Sept. 22: You put down on the streamer issue and pick up on a good latch for the gate to your front yard.

SE in slang uses

In phrases

latch for the gate to your front yard (n.)

(US black) fly buttons or a collar pin.

1944

D. Burley Orig. Hbk of Harlem Jive 142: Latch for the gate to your front yard — Collar pin.