Found this 1966 with no mint mark, and on the obverse side faint letters in E Pluribus and states of along the top. Also the L in liberty is along the edge.
No cents in 1966 had a mint mark, so that is normal. Weak letters on the reverse is nothing special either. Could be 52 years of wear, or they may have been weak when the coin was struck due to a partially filled die.
Actually all 3 mints produced coins with no mint marks in 1965 1966 and 1967. So there's no way to tell which one it came from during those 3 years. But all the other no mint mark coins are always Philadelphia.
I think I saw somewhere that they did this to anger the collectors because the collectors were angry that they weren't making silver coins anymore. Therefore, collectors couldn't tell where it was from and so they couldn't really collect all three mint marks for the three years.
There was hoarding going on, because of the elimination of silver in the coins. And, they felt people were taking out all the mint marked coins creating a coin "shortage". So they passed some act to eliminate the mint marks on coins, which of course came back in 1968.
