All Australian Pennies from 1938 to 1964 had the initials KG just above the tail of the kangaroo.
It is not a mintmark, it is the initials of the designer of the reverse side of the coin, George Kruger Gray.
On a 1951 Australian penny, the mint mark is located on the reverse side of the coin, just below the kangaroo. If the penny was minted in Melbourne, it will have no mint mark. If it was minted in Perth, it will have a "P" mint mark, while those minted in London will have an "H" mint mark.
2002 mint sets in original package have a value of $15.00 to $20.00. The penny has never had a P mint mark.
The mint mark does not determine the value of a coin. If you have a penny and want to know what it is worth, please submit a new question and include the date on your penny as well as the mint mark.
A 1914 penny with no mint mark is worth about $1.50.
So very many were made is just a penny
A 1943 steel penny with no mintmark can be worth $.35 - $1.50
The Australian 1943 Penny was minted variously at the Melbourne Mint (no mintmark), Perth Mint (mintmark is a dot after the Y in PENNY "Y.") and Bombay Mint (mintmark is an "I" under King George's bust).
Value will vary depending on condition and mint mark. About $0.35
The lack of a mint mark means it was struck in Philadelphia, and value is 1 cent.
Regardless of which mint mark it has, values are 5 to 10 cents. Uncirculated coins are a dollar or less.
8 to 20 cents depending on condition.
It is worth face value.