Green’s Dictionary of Slang

1. (Aus.) hello! an excl. of welcome and support.

1965

D. Martin Hero of Too 339: He waved his hat. [...] The gesture was well received. ‘On yer, Klep!’ Tooramit and Boobyalla united in a great outburst of democratic pride.

2. a general excl. of rejection.

1965		E. Bond Saved Scene x: barry: Wipe yer boots. mike: On you!
1990		R.G. Barratt ‘Jaws 5’ in What Do You Reckon (1997) [ebook] ‘Saw a big shark, did you? [...] Onya, Barrett. Frightened by your own shadow’.