Green’s Dictionary of Slang

(Aus.) a relatively unsophisticated person who attempts to ape the supposedly smart style of an American.

1947		Sun (Sydney) 18 May 3/6: On the [USN] flag ship Shangri-la, the crew have been studying the Australian language from a special slang glossary [...] A ‘Woolloomooloo Yank’ or a ‘Fitzroy Yank’ is described as a ‘flashy dresser’.
1954		Argus (Melbourne) 25 Nov. 3/5: Why the spate of ‘Fitzroy Yanks’ on our radios? Sev eral stations now have pseudo- Americans mixing the ‘waa-als’ with the ‘rawthers.’ Hope this Is no taste of more to come.
a.1970		Phil Motherwell [play title] Fitzroy Yank.