Green’s Dictionary of Slang

1. (US Und.) an initiate into criminality; a thief [a metaphor taken from freemasonry].

1914

Jackson & Hellyer Vocab. Criminal Sl. 44: hiram [...] a metaphor taken from masonry [i.e. freemasonry] to signify initiation into the secrets of the yegg profession. A synonym for yegg.

2. (US) a rustic, a peasant [the proper name, used in the Old Testament and thus popular among Puritan immigrants].

1912		T.A. Dorgan Daffydils 31 Dec. [synd. cartoon strip] Hiram came all the way down from Hosh Kosh Manor to get a squint at the warships in the Hudson river.
1931		Irwin Amer. Tramp and Und. Sl. 99: HIRAM.– [...] many of the oldtime yeggs preyed upon the country post offices in the districts populated by farmers or, traditionally, ‘Hirams.’.
1942		Berrey & Van den Bark Amer. Thes. Sl. §391.3: rustic, bumpkin, Hiram.
1989		H. Rawson Dict. of Invective (1991) 192: As for country dwellers, in addition to hick, names and nicknames that have been used disaparagingly as generics include: [...] Hiram.