1990 D Lincoln Cent, Misplaced Mint Mark

I'm not seeing any mint mark (consistent with a Philadelphia minted cent). That somewhat round feature to the left of the date appears to me to be a stain or died droplet of gunk. Is the feature in question raised, flush, or sunken (incuse)?

It is slightly raised. Looks quite a bit to me like a D mint mark from the Denver mint.

No possible way for it to be a misplaced mint mark as starting in 1990, any mint mark was part of the master die, and was not placed by hand as in previous years. This is most likely something that got onto the coin and caused some slight corrosion of the copper plating, staining it and giving it a very slightly raised feel. I can see several other smaller, similar looking stains on this coin as well.

Dave42 .. I didn't know that, as you say, in 1990 the mint mark was part of the master die. That would tell me that it couldn't be a misplaced mint mark. Unless it was an early 1990 that was done before they started doing it that way, which is, of course not possible. Right?

When you look into how the minting process works, you will find that misplacing a mint mark when a coin is minted is a physical impossibility.

While the bubble resembles a D, there is no way this coin could physically have been made at the Denver mint. B/c of the above fact.

Look for videos online about making coins...especially the dies. The videos are fun to watch :)

That means that it is a normal business strike from the Philadelphia mint because it really doesn't look like a proof from San Fran.

Correct. if it were a proof - there would be an S mint mark on it For San Francisco.

If it was a sneeze that was later cleaned, the stain would verify you cannot just clean away stains. Never never clean your coins! Many a coin have been ruined value wise by cleaning.

All that said, what you have here is not a misplaced mintmark. On cents, the last mintmark placement by hand was 1989. Only quarters had their mintmarks placed by hand in 1990, and your coin was not mistaken for a quarter, sorry. Your coin has a broken plating bubble in which the next stage is zinc rot. Spend it while you still can!