Many people collect coins. And as anyone that has collected coins will know, different coins made in countries will often have a mint mark.
In the United States, there are mint marks that represent the different U.S. Mints where they were produced. There is a P for the Philadelphia Mint, and an S for the San Francisco Mint. But sometimes the mint mark is omitted, and if that happens this means that it was made in Philadelphia, as the Philadelphia mint mark is sometimes left off.
There are other Mint marks that are less frequently seen but that are present on different U.S. coins. C is for Charlotte, N.C., if you see a W is is for the West Point Mint. No mark is for Philadelphia, PA mint, as is the letter P.
If you see a D, you have an old coin, it is for the Dahlonega Georgia mint that produced coins from 1838 to 1861, and a O is for the New Orleans LA mint. A double CC means Carson City Nevada, and a D means the Denver Mint.
A mint mark shows where the coin was made, and it is valued by coin collectors because coins that are produced in different locations often have different value.
This is because coins are made in different numbers, and with different designs. Because of this, their scarcity, or availability affects their ultimate long term value.
If a coin is scarce or hard to find it will be more valuable, and have more long term value to a collector, while if a coin is very common it will have a lower overall value.
Coin collecting can be very fun, and knowing what the mint marks are can mean the difference between coin identification of a lot of different types of coins.