Green’s Dictionary of Slang

1. scissors.

1821

J. Burrowes Life in St George’s Fields 14: Bill placed his canister under the thieving-irons.

2. hands.

1821		‘Miscellaneous’ in Fancy I IV 102: Then did Mary, sweet Mary, bring her thieving-irons together with such wondrous force, that some one taking the hint she had given, put something in her hands.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 106: ‘Thieving irons,’ the hands of rogues; and the forefinger should be as long as the middle one. With this purpose in view, they pull their forefingers daily and hourly, and let the nail grow long.
1910		Banffshire Advertiser 1 Sept. 7/2: Upon my word! a famous haul for Reuben Gill to lay his theivingirons upon.
1919		W.H. Downing Digger Dialects 49: thieving irons — Hands.
1924		(con. WWI) A.G. Pretty Gloss. Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: theiving irons [sic]. Hands.