What is a Mint Mark?

A Mint Mark indicates the mint which produced the particular coin or coin set.

What are the mint marks and what do they stand for?

The mint marks are:

C = Charlotte, NC (gold coins only, from 1838-1861)

D = Denver, CO (1906 to date)

D -= Dahlonega, GA (gold coins only, 1838-1861)

S = San Francisco, CA (1854 to date)

CC = Carson City, NV (1870-1893)

O = New Orleans, LA (1838-1861 and 1879-1909)

W = West Point (1984 to date)

The one very unique mint mark/identifier is actually no mark at all, at least in the older coins.

That would be the "P" mint mark, which stands for the Philadelphia mint (1793 to date, P not used in early years)

Prior to 1979 the P was absent from coins struck in Philadelphia, so NO mint mark meant Philadelphia.

In 1979, with the advent of the Susan B. Anthony dollar, the "P" began appearing as a struck mint mark on coins; this does not appear on the cents.