Green’s Dictionary of Slang

rumbo-ken n.

a pawnshop .

1724		‘Frisky Moll’s Song’ in J. Thurmond Harlequin Sheppard 22: He broke thro’ all Rubbs in the Whitt, / And chiv’d his Darbies in twain / But fileing of a Rumbo Ken, / My Boman is snabbled again.
1728		Defoe Street Robberies Considered 34: Rumbo Ken, Pawn-Brokers.