Green’s Dictionary of Slang

1. a pilferer, a petty thief; a pickpocket.

1802		Sessions Papers Apr. 288 in DU.
1882		Star (Guernsey) 23 Feb. 4/2: Friskers are tolerably well-dressed young fellows who frequent the leading business streets [of London] Two or three of them will hustle you into a corner.
1904		Phila. Inquirer 22 May Pt II 3/5–6: ‘Frisk’ is a new word which is attaining wide popularity in certain circles. It means ‘to go through one.’ Thus, a gentleman who has been made the victim of personal robbery has been ‘frisked.’ A ‘frisker’ is in plain language a thief, though the term is becoming elastic and may mean a form of skylarking.
1911		S. Ford Torchy 62: He’s a common, everyday, free lunch frisker, Mac is.
1922		T. Thursday ‘Ten Dollars – No Sense’ in Top-Notch 15 Dec. 🌐 ‘Silk-hat George,’ the famous international flat frisker and grade-A con man.
1929–31		in W. Kernot unpub. gloss. of US cant in DU.
1949		Monteleone Criminal Sl. (rev. edn).

2. (UK Und.) one who conducts a body search.

1865

Leaves from Diary of Celebrated Burglar 7/2: All eyes seeming to turn towards ‘Dublin Joe’ he ‘tumbled’ to the ‘rachet’ and offered himelf first for the ‘frisk,’ old Charley Potter [...] officiating as ‘frisker’.