Coins made at the Philadelphia mint did not have mint marks
until the 1980s. Your coin was made at the Philadelphia mint.
View page
At the Philadelphia Mint.
View page
If a penny has no mint mark, it typically means it was produced by the Philadelphia Mint. Mint marks indicate where a coin was minted, and coins from the Philadelphia Mint, the oldest U.S. Mint facility, do not have a mint mark.
View page
A Philadelphia coin known as a Philadelphia mint is a coint that
is made that has a P on it for penny. The Philadelphia mint coin is
worth about one sent.