Green’s Dictionary of Slang

1. (US) a dollar.

1941		C. Brackett & B. Wilder Ball of Fire [film script] The accepted vulgarism for a smackaroo is a dollar. That goes for a banger, a fish, a buck or a rug.
1947		S.J. Perelman ‘Farewell, My Lovely Appetiser’ in Keep It Crisp 13: She trailed past me in a cloud of scent that retailed at ninety rugs the ounce.

2. (Aus.) a £1 note.

1943		Baker Popular Dict. Aus. Sl. (2nd edn).
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 7: ‘What is the ask,’ he said [...] ‘Twenty rugs,’ she smiled showing a couple of Barrier reef missing from between her painted penny dips.