How to Determine Were an Australian Coin Was Minted
All Australian general circulation coins have been minted at the Royal Australian Mint Canberra since 1984. Non-circulating Legal Tender coins are minted at both the RAM Canberra and the Perth Mint.
Mint Marks on Australian decimal coins are mostly minute differences to the reverse design like a blunted first whisker or second claw, or a longer spine, etc. Those not minted in Australia, were minted at the Royal Mint London or Wales.
Predecimal coins are more difficult to identify because they are inconsistent from year to year and from coins of different denomination. A dot after the "A." in AUSTRALIA, a dot after the "Y." in PENNY or a dot between "K.G" (the designers initials) indicate minting at Perth.
Those coins not minted in Australia will have a small letter usually on the reverse but not always, indicating where it was minted.
So, depending on the coin, the coin has been released in:
"L" and "PL" - London,
"I" = Calcutta or Bombay,
"H" = Heaton, Birmingham,
"S" = San Francisco,
"D" = Denver.
Occasionally "M" = Melbourne or a small star "*" for Sydney, but usually Melbourne and Sydney did not have Mint Marks.