Green’s Dictionary of Slang

a counterfeit coin.

[1718		A. Ramsay Lucky Spence’s Last Advice [ballad] Ye’r face will not be worth a Feg, nor yet ye’r Tail].
1798		M. Edgeworth Practical Education I 315: Coiners give regular mercantile names to the various kinds of false money which they circulate; such as flats, or figs, or fig-things .
1884		A. Griffiths Chronicles of Newgate 319: Figs, or fig things, were the lowest and meanest class [of counterfeit silver coins] and was confined chiefly to sixpences.