Here is a proof; Notice the square rims, the cameo, the solid strike, and the shiny fields. You coin has none of the above.
My source is the proof coin. Yours has no mirrored fields, rims that are not squared, and poorly struck devices. What you have is a 1990-P. They didn't have a mintmark on the Philly coin. Chris
My cent does not have the mint S. Although your picture does. From what I read there is only 200 to be found?
Venture out onto the Internet or even EBay and study the pictures of Lincoln proofs. You'll see what others are talking about.
That is interesting. Not only did PCGS grade 185 of them, but NGC has 76. Granted some of those have got to be re-submits, but I will also be there are some not yet submitted, some by other companies, some not yet even found, etc.