Green’s Dictionary of Slang

(UK Und.) a criminal beggar, posing as a legitimate pedlar.

c.1561		Awdeley Fraternitye of Vacabondes in Viles & Furnivall (1907) 5: A Swygman goeth with a Pedlers pack.
1608		Dekker Belman of London D3: Like vnto him [the Irish Toyle] in condition is a Swig-man or Pedler, carying a packe behind him in stead of a wallet: their trades are all one, saving that the Swigman is somewhat better in behauiour, though little differing in honefty.
1669		W. Winstanley New Help To Discourse 134: Swig-men, are such as we call Pedlars, who carry a pack at their back, and are little different from the Irish toyls.
1674		Head Canting Academy (2nd edn) 58: These Irish-Toyls or Swig-men being much alike, I joyn them together, who carry points and laces, and such like wares about; who under the pretence of selling such Commodities, commit many Rogueries.
1688		R. Holme Academy of Armory Ch. iii item 68b: Give me leave to give you the names (as in their Canting Language they call themselves) of all (or most of such) as follow the Vagabond Trade, according to their Regiments or Divisions, as [...] Swigmen, cheaters by changing of wears.
c.1698		B.E. Dict. Canting Crew n.p.: Swig-men, the 13th Rank of the Canting, carrying small Habberdashery-Wares about, pretending to sell them, to colour their Roguery.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1749		B.M. Carew ‘The Oath of the Canting Crew’ in Farmer Musa Pedestris (1896) 51: No swigman, swaddler, clapperdudgeon; / Cadge-gloak, curtal, or curmudgeon.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: swigmen, Thieves who travel the country under colour of buying old shoes, old clothes, or selling brooms, mops (cant).
1809		G. Andrewes Dict. Sl. and Cant n.p.: swigg-men thieves who travel the country under the colour of buying old clothes, &c.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1835		G. Kent Modern Flash Dict. 32: Swigsmen – thieves who travel the country under cover of buying old clothes.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].
1859		Matsell Vocabulum 88: swig-coves Fellows who traverse the country under the pretense of begging old clothes.