Green’s Dictionary of Slang

(US) a $1 coin.

1919		Amer. Legion Weekly 11 Jan. 24: I’ve gota job waiting for me that pays thirty moons a week instead of thirty a month [...] Thirty discs. That’s sure beaucoup l’argent [HDAS].
1969		D. Pendleton Executioner (1973) 97: Its all organization money, every nickel of it. What’s he got to cry about? The discs were mine, not his.