Green’s Dictionary of Slang

sixpence (2½p).

1859		Hotten Dict. of Modern Sl. etc. 127: EXIS-YENEPS, sixpence.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 23/1: Exis-yenep ... Sixpence.
1873		Sl. Dict.
1935		R.T. Hopkins Life and Death at the Old Bailey 65: Costermongers invariably use the following terms in discussing money transactions [...] Exis-yenep – Sixpence.