Mintage data for 2006 Lincoln cents:
The Philadelphia Mint struck 4,290,000,000, Denver 3,944,000,000 and 3,054,436 Proof coins were struck at the San Francisco Mint.
Pennies are minted at three locations in the US; The San Francisco Mint, The Denver Mint and the Philadelphia Mint. Pennies from San Francisco have an "S" on them. Pennies from Denver have a "D" on them and pennies from Philadelphia have no letter.
Because it costs more than a penny to produce a penny.
In 2011, the U.S. Mint produced 4,938,540,000 pennies.
Company that makes pennies
Australian Pennies from 1955 to 1964 inclusive were minted at either or both of the Melbourne Mint and the Perth Mint. Pennies minted at the Melbourne Mint have no mintmark. 1956 Pennies minted at the Perth Mint can be identified by a dot "." after the "Y" in PENNY, eg. "PENNY.".
Company that makes pennies
At the Philadelphia Mint.
1938 IN a MINT
Australian Pennies from 1955 to 1964 inclusive were minted at either or both of the Melbourne Mint and the Perth Mint. Pennies minted at the Melbourne Mint have no mintmark. Pennies minted at the Perth Mint can be identified by a dot "." after the "Y" in PENNY, eg. "PENNY.". In other years, Perth Mint Pennies can also be identified by a dot after the "A" in AUSTRALIA, eg. "AUSTRALIA." or, a dot between the designers initials "K.G".
Australia struck pennies in 1955 at two locations - the Melbourne Mint and the Perth Mint. The Perth Mint pennies have a very small dot, to the right and in line with the base of the "Y" in "PENNY" on the reverse / tails side. The pennies struck at the Melbourne Mint do not have this dot.
In general, "S" mint marks from the San Fransisco mint are more scarce than other mint marks when it comes to pennies. But just because it has an "S" on it doesn't make it a rare, or even scarce coin.