Character. He stood a queer lock; he bore but an indifferent character. A lock is also a buyer of stolen goods, as well as the receptacle for them.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
See also the definition in Nathan Bailey's 1736 dictionary of canting and thieving slang.
Lock * Lock HospitalNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes