Green’s Dictionary of Slang

1. a pickpocket whose speciality is stealing silk handkerchiefs.

1708		J. Hall Memoirs (1714) 5: Clouters, Such as take Handkerchiefs out of Folks Pockets.
1718		C. Hitchin Conduct of Receivers and Thief-Takers 12: Sir, those Boys are all Clouters, alias Pick-Pockets, and that Man in the silver-button’d Coat, is their Thief-Taker.
1839		(con. 1715) W.H. Ainsworth Jack Sheppard (1917) 141: Next to these hopeful youths sat a fence, or receiver, bargaining with a clouter, or pickpocket.

2. (US Und.) a shoplifter.

1909

F.H. Tillotson How I Became a Detective 90: Clouter – A shoplifter.

3. a thief.

1950		Goldin et al. DAUL 46/1: Clouter. A thief, especially one who eschews force.
2023		(con. 1962) J. Ellroy Enchanters 322: ‘Listen, papa-san — you were a watch clouter way back when’.