Green’s Dictionary of Slang

snam v.

to steal, to pilfer; thus snamming n.

1839		H. Brandon Dict. of the Flash or Cant Lang. 165/2: To Snam – to snatch.
1857		in ‘Ducange Anglicus’ Vulgar Tongue.
1861		Bell’s Life in Sydney 2 Mar. 3/3: [She] said ‘see what I have copped’ by which she understood that she had ‘snammered’ it.
c.1863		gloss.fs in Occurence Book of York River Lockup in Seal (1999) 37: Was a mushroom faker, has been on the steel for snamming a wedge sneezer so I must hoop it.
1873		Sl. Dict. 298: Snam to snatch, or rob from the person. Mostly used to describe that kind of theft which consists in picking up anything lying about, and making off with it rapidly.
1881		Newcastle Courant 25 Nov. 6: Just before bolting I snammed these out of the yokuff we’d just opened.
1882		Sydney Sl. Dict. (2 edn) 8: Snam - To snatch.
1895		Crowe Aus. Sl. Dict. 77: Snam, to snatch from the person and then run off.

In phrases

upon the snam

engaged in thieving.

1887

W.E. Henley ‘Villon’s Good-Night’ in Farmer Musa Pedestris (1896) 175: For you, you coppers, narks, and dubs, / Who pinched me when upon the snam.