Green’s Dictionary of Slang

ah sin n.

(Aus.) a generic term for a Chinese person.

[Aus]Bulletin (Sydney) 15 Oct. 8/3: But one doomed Ah Sin escaped his notice and went into the swamp to hunt for something – Confucius only knows what; fish, very likely; frogs, perhaps; probably crabs – and was caught.
[Aus]Truth (Sydney) 8 July 4/7: They are great at running in / Any Bushy on the rantan / And they swoop upon Ah Sin / Playing childish games of fantan.