Susan B $1 missing the S at the end of States. Does this look like a strike through error, or PMD? It is just the S and a little bit of the E that is missing. A little bit of the bottom of the S is visible, but only with a microscope.
Struck through. You really don't need a microscope to see the bottom of the S.. Just use plain eyesight and picture it in your mind.
Welcome to CT. It could very well be a strike through. However, I see what appears to be an awful lot of 'activity' in the field in and around where the S should be. Possible PMD (Post Mint Damage) by intentional manipulation?
I felt the same way until I saw that last photo. Looks like a piece of cloth was on the planchet or die when it was struck.
My first impression was PMD. Someone intentionally did it, but like some others here suggest, it could very well be struck through. A small piece of cloth or paper got between the die and the planchet when it was struck. Good eye. Welcome to CT and good luck.