Question: I have a 1942 mercury dime with a mint mark of "W". Where is that, and why don't I ever see it listed when I read prices of coins?

Answer: It's actually not a mint mark, but a very prominent display of the designer's initials - Adolph A. Weinman. If you look closer, what looks like the letter W has an A in it.

The mint mark on the Mercury Dime is located on the reverse to the left of the fasces and to the right of the 'E' in ONE.