Green’s Dictionary of Slang

(US) affected, pretentious.

1896		Ade Artie (1963) 57: I guess it was n’t put on, though. She was probably broke up.
1930		N. Lindsay Redheap (1965) 18: Peter at least [...] considered that this voice of Ma’s was ‘put on’.
1948		C. Day Lewis Otterbury Incident 32: He talked in a put-on American accent.
1952		J. Jones From Here to Eternity (1998) 651: Prewitt, who was not a Jew, and who shamed you with that big put-on act of his being perfect.
1973		(con. mid-1960s) J. Patrick Glasgow Gang Observed 89: In the language of the Gorbals, he was ‘well put on’ and proud of his ‘paraffin’.
1974		Adamson & Hanford Zimmer’s Essay 20: Helm’s strine shifted into a put-on pommie drawl: ‘My dear fellow’.
2001		I. Welsh Glue 69: Hurry along now boys, you’ll be late for school! eh goes n a high, pit-oan posh voice.