How can you tell where an Australian Halfpenny was minted?

The Mint Marks for Australian Halfpennies are usually on the reverse.

From 1911 to 1939, the reverse had the words "ONE HALF PENNY" above a small scroll within a circle. Between the circle and the outer edge of the Penny, the words "COMMONWEALTH OF AUSTRALIA" were inscribed around the circumference with the year at the bottom.

All Pennies from 1911 to 1915 inclusive with no Mint Mark from were minted at Royal Mint, London. All Pennies from 1919 onwards with no Mint Mark were minted at the Melbourne and Sydney Mints on identical dies. An "H" above the year indicates the Heaton Mint in Birmingham, England (1912, 1914 and 1915 only). An "I" above the year indicates the Calcutta Mint, India (1916, 1917 and 1918 only). The Mint Mark is above the year inside the inner circle.

From 1939 to 1964, the Halfpenny had a right facing hopping kangaroo with the word "AUSTRALIA" around the circumference at the top and the word "HALF PENNY" around the circumference at the bottom. The year is below the kangaroo's body and the Commonwealth Star is below the kangaroo's head.

A dot after the the "Y." in HALF PENNY or the "A." in AUSTRALIA or between the designers initials "K.G" indicates the Perth Mint. A "PL" below the year indicates the Royal Mint, London (1951 only). An "I" below King George VI's neck indicates the Bombay Mint in India (1942 and 1943 only). All other Halfpennies were minted in Melbourne and have no Mint Mark.