Although I've never seen an official Australian hallmark, they did exsist. The Commonwealth of Australia Hall-Mark Company was opened in 1923 at the Sydney Assay Office, the marks were as follows:
Kookaburra for Gold,
Wren for Silver,
The fineness of each metal was distinguished by numerals, the Kookaburra and Wren were struck in oblong punches with clipped corners as follows:
Mark with corners intact: New South Wales,
Mark with right top corner clipped: Victoria,
Mark with left hand bottom corner clipped: Queensland,
Mark with left hand top corner clipped: South Australia,
Date letters were also stamped starting with A=1923.
In the first nine months New South Wales marked 13,712 articles of Gold and 1,061 articles of Silver, destroying 587 items that did not pass the assay test.
How long the assay office lasted, I do not know, it wouldbe good to know some more information.