Persons who pretend to be smugglers of lace and valuable articles; these men borrow money of publicans by depositing these goods in their hands; they shortly decamp, and the publican discovers too late that he has been duped; and on opening the pretended treasure, he finds trifling articles of no value.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Smug * Smuggling KenNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes