There isn't one. All cents were struck at Philadelphia until 1908. In that year and 1909 some Indian head cents were struck at San Francisco; the mint mark appears on the reverse below the wreath.
When the Lincoln design was introduced in 1909 the mint mark was placed below the date. This was only the second design to regularly have its mint mark on the obverse; the first was the short-lived $2.50 gold piece "Classic Head" design issued from 1834 to 1839.
Lincoln cents have been minted at Denver, San Francisco, Philadelphia, and West Point. The first 2 have mint marks D and S. Cents from Philadelphia and West Point continue the old practice of not using mint marks, primarily because production at West Point is on an as-needed basis. The Mint does not want to create instant rarities by minting, say, a few million 2008-W cents while the other mints churn out billions.
A 1943 steel penny with no mintmark can be worth $.35 - $1.50
A 1941 penny without a mintmark means it was minted in Philidelphia.
A US Lincoln cent with no mintmark was made in Philadelphia.
Average value is 3 to 10 cents.
Please be more specific, which mintmark?
There is no mintmark on the 1921 British Penny, they were all minted at the Royal Mint London.
A mintmark is a small identification mark used to tell which mint it was made in.
underneath the year
It will have a S mintmark.
An Australian Penny or Halfpenny with a "Y." (PENNY.) mintmark indicates that the coin was minted at the Perth Mint. An Australian Penny or Halfpenny with a "I" mintmark indicates that the coin was minted at either the Calcutta or Bombay Mints in India.
Philadelphia. Cents (pennies) from the Philadelphia mint have never carried a mintmark.
A 1943 steel penny with no mintmark can be worth $.35 - $1.50
If it has one , it's under the date
An Australian 1956 Penny looks almost exactly the same as any other Australian Penny minted from 1955 to 1964 inclusive. A 1956 Penny minted in Perth will have a mintmark (.) after the "Y" in PENNY (Y.). The Melbourne Penny has no mintmark. See the 1964 penny at the link below.
A 1941 penny without a mintmark means it was minted in Philidelphia.
KG is not a mintmark, it is the initials of the designer of the (kangaroo) reverse of the Australian 1938 to 1964 Penny and Halfpenny coins, George Kruger Gray. 1940 and 1941 Pennies minted at the Perth mint have a dot between the K and the G (K.G) as the mintmark.
All British Pennies from 1883 to 1911 inclusive have no mintmark. They were all minted at the Royal Mint London.