Green’s Dictionary of Slang

(US) an insignificant person, esp. a low-level employee.

1959		L.P. Boone ‘Gator Sl.’ AS XXXIV:2 154: The opposite of a B.M.O.C. is a loser, gnome, mullet, or spook.
1966		Current Sl. I:2 3/1: Gnome, n. A campus employee, esp. janitors, ground helpers, kitchen help.