Green’s Dictionary of Slang

a shoplifter’s assistant, to whom the stolen goods are quickly passed by the actual lifter; 20C use refers to any shoplifter.

1663		Wandring Whores Complaint 5: The tenth is a Shop-lift that carries a Bob, / When he ranges the City the Shops for to rob.
1671		‘L.B.’ New Academy of Complements 204: The tenth is a Shop-lift that carries a Bob, / When he ranges the City the Shops for to rob.
c.1698		B.E. Dict. Canting Crew.
1719		A. Smith Lives of Most Notorious Highway-men, etc. (1926) 203: Bob, a shoplift’s comrade, assistant, or receiver.
1725		New Canting Dict.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1725].
1754		Scoundrel’s Dict.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1813–82		B.M. Carew Life and Adventures.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
1859		Matsell Vocabulum.
1881		Trumble Sl. Dict. (1890).
1895		Crowe Aus. Sl. Dict. 10: Bob, [...] a shoplifter.
1927		‘Jargon of the Und.’ in DN V 439: Bob, A shoplifter.
1931		Irwin Amer. Tramp and Und. Sl. 32: Bob. – A shoplifter. One of these individuals has declared that the manner in which he and his kind ‘bobbed’ in and out of a crowd looking for an opportunity to pilfer gave raise to the word; certainly the origin is no more far-fetched than many another underworld idea.
1949		Monteleone Criminal Sl. (rev. edn) 29: bob A shoplifter.