Green’s Dictionary of Slang

a sovereign.

1886		Sporting Times 4 Sept. 5/3: George Fredericks estimates the damage in glass at about four spangles and half an ames-jay,.
1886		J.B. Booth Sporting Times 21 Aug. 1/2: I’d ’ardly got a touch-me in my sky, much less an amesjay to pay for me saint an’ sinner!