Green’s Dictionary of Slang

harman n.

also beck-harman, harman-beck, harminbeck
[ety. unknown; ? OED suggests elision of SE hard-man; DSUE prefers ha-man, i.e. one who shouts ha!, stop; ult. dial. har, stop! + SE beck, beak]

1. [mid-16C–19C] (UK Und.) a constable.

2. [late 17C–19C] a beadle.

3. [mid-19C] a sheriff.