1990 Penny With A Really Big S With No Mint Mark

No mintmark = Philadelphia, as the original mint, they only used the P mintmark for the War Nickels (1942-1945) to show they were 35% silver.

And then in 1979 with the Susan B. Anthony dollars followed by all regular coins 1980 and later from the nickel up.

The 2017 Lincoln Cent is the only Lincoln Cent with a P mintmark to commemorate the 225th anniversary of the founding of the mint.

Now if you want to chat about American Silver Eagle Bullion coins (ASEs), yes, there are a bunch of shenanigans with the P mintmark there.