Green’s Dictionary of Slang

(US Und.) counterfeit banknotes; thus coney man, one who passes counterfeit notes; coney traffic, coney business, counterfeit money trafficking.

1823		‘One Who Knows’ Inside Out; or, An Interior View of the N.-Y. State Prison 107: Counterfeit money, is called, among Sharpers, by the slang name of Cogniac [...]. [Ibid.] 108: A fellow, [...] when he has been a little unsuccessful at Thieving, passing Cogniac to defray his expenses.
1840		N.Y. Herald 15 Jan. 2/5: It seems almost a miracle that the catchers did not escape, as they were not detected until they were getting off the last ‘drop of Cogniac’ in their possession.
c.1858		J.H. Green Secret Band of Brothers 113: The word coney means Counterfeit paper money.
1872		G.P. Burnham Memoirs of the US Secret Service 52: I always had bogus money in plenty [...] I controlled the market for ‘coney’. [Ibid.] 95: All the ‘coney men’ rushed to New York to obtain bundles of this admirable specimen of the ‘queer’. [Ibid.] 99: He ‘acknowledged the corn,’ owned up fairly to having been in the coney traffic a long time.
1882		A. Pinkerton Professional Thieves and Detectives 24: You helped break up the ‘coney men’ and horse-thieves on ‘Bogus Island’.
1886		A. Pinkerton Thirty Years a Detective 531: The ‘twenties’ [dollar note] were excellent [...] and placed him at the head of the ‘Coney’ business as a cutter or engraver.
1906		Cameron Co. Press (PA) 29 Mar. 6/3: The stranger confided his criminal history and desire to handle ‘coney’. He combined preaching with larceny [...] and those of ‘koniacker’ .