Green’s Dictionary of Slang

(orig. US) a general term of affirmation, OK, that’s right, everything’s in order.

1922		S. Ford Trilby May Crashes In iii. 54: ‘I have felt all along that’ ‘Check!’ says I. ‘I get the picture.’ .
1936		(con. 1920s) Dos Passos Big Money in USA (1966) 786: ‘My name’s Bobbie . . . you call me Bobbie, won’t you?’ ‘Check,’ said Charley.
1940		R. Chandler Farewell, My Lovely (1949) 39: ‘You are Philip Marlowe, a private detective?’ ‘Check.’.
1952		J. Jones From Here to Eternity (1998) 638: ‘Do it at chow this noon.’ ‘Check,’ Prew said.
1963		A.S. Fleischman Venetian Blonde (2006) 158: You’re going to go your way, and I’m going to go mine [...] Check? Okay? Right?
1977		‘John le Carré’ Honourable Schoolboy 459: ‘Check,’ said Murphy.
1988		D. Woodrell Muscle for the Wing 8: ‘Scoop the fuckin’ manna, boys.’ ‘Check,’ said Dean Pugh.
1998		I. Welsh Filth 87: Check, Ray says, exciting.