scan, v. — Green’s Dictionary of Slang

scan v.

to see, to notice; thus scanner n., an onlooker, a surveyor.

1568		U. Fulwell Like Will to Like 41: I fear that, when that this gear shall come to scanning, The land to the which we did wholly trust: Shall be gone from us.
1812		W. Combe Doctor Syntax, Picturesque (1868) 83/2: If I can scan / The temper of the gentleman, / He’s one of those, I have no doubt, / Who loves to let his humour out.
1821		W. Combe Doctor Syntax, Wife (1868) 332/1: ‘O,’ she exclaim’d, ‘the truth I scan; / When he grows up he’ll be a man.’.
1837/8		‘Wry-Mouth Bob And His Jolly Red Nob’ Cuckold’s Nest 46: When a female wandered to his stall, / His long tool would display, / Then her leather he’d scan, like a jolly good man, / And at it he’d lather away.
1862		J.A. Hardwick ‘Whitechapel v. Westminster’ Prince of Wales’ Own Song Bk 21: So much for the East, so much for the West, / Of both I’ve been a scanner.
1908		‘Doss Chiderdoss’ ‘Penny Numbers’ Sporting Times 11 July 1/3: I happened to scan / Something no one would pass by unheeded. / A young woman, your worship, as fair to the sight / As—I’m not a descriptive reporter.

scan on (v.)

(US black) to watch closely, to look closely, esp. at something one intends stealing.

a.1967

‘Sporting Life’ in D. Wepman et al. Life (1976) 162: There’s the cool old shot at the busy bus stop / Scanning on a hide.