National dealer

My coin is missing a Mint mark, words, letters or numbers. Where did they go?

Your coin most likely features a filled-die error

A filled die is a very common form of error and does not add value to the coin. Filled die errors are known on every series of coin ever struck by the U.S. Mint.
You should also know that many U.S. coins do not bear mintmarks on purpose. All coins struck at the Philadelphia Mint from 1793 to 1978 lack Mint marks, except for some 1942 to 1945 5-cent coins. Beginning in 1979, Anthony dollars struck at the Philadelphia Mint carried a P Mint mark. In 1980, the P Mint mark was added to the 5-cent coin, dime, quarter dollar, and half dollar struck in Philadelphia. However, none of the Lincoln cents struck at Philadelphia bear a Mint mark.

Dima

Interestingly enough, the lack of a P mint mark on pennies allowed the government to mint pennies at West Point without a W or P mint mark in the 1980s. The composition of these pennies is, obviously, the same from both West Point and Philly and they are impossible to tell apart. My favorite part of this story is that the pennies were minted at West Point before West Point was officially declared a branch of the US Mint. Further reading.

Kind of off-topic, but nonetheless.

Cheers!

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When I was a little boy my mother always told me that I was her million bucks; I always told her I'd rather be her 1913 V nickel. Some day I'll marry a girl who I'll certify as PR70DCAM. Maybe she'll be toned nicely...?