Where Is a Mint Mark on a Penny?

By GovMint :

The mint mark on the iconic Lincoln Cent is on the obverse of the coin. The identifying mark is located below the year, between Lincoln's chest and the coin's rim. The placement of the mint mark has not changed from the beginning of the series in 1909. The San Francisco Mint struck cents through 1955. The Mint began striking cents with the S mint mark again from 1968 through 1974. The Denver Mint has struck cents throughout the series. 

 A famous, if stealthy, exception to the "Philadelphia has no mint mark on cents" rule is the 2017-P Lincoln Cent. The Mint made no prior announcement that they would include a P mint mark as a way to mark the 225th Anniversary of that fabled coinage facility. In 2018, the P vanished again, as one would expect.

Sources Used:

https://www.interestingfacts.com/fact/6386d2b1bd1439000808d979

Concept of the Month: Fun Facts About Coins - Young Americans Center (yacenter.org)