I still see nothing on your original posted coin, however, the 2nd coin you posted clearly shows a faint "S".
They may have only looked at the coin for 10 seconds and did not spend an hour with an electron microscope on a beat up 1932 quarter. And my theory was just a guess. Don't ask for opinions and then disagree with the ones you don't like. If there is a ghost image of an S which is not an illusion, than that coin may have had an S affixed to it at one point.
Don't give an opinion and not expect to be asked how it was conceived. I don't own a microscope, electron or otherwise, and my loupe has electrical tape holding it together, but my eyes work pretty good and I don't believe there is an obstruction between them and my brain.
Ok guys if you sit back from your computer you can see it very clearly it's either a D or a S and yes its there.
The way the human brain works is to match patterns: That shape in the tall grass looks like a lion... avoid. Your brain creates patterns out of partial information where they may not exist. It's an incredibly powerful vision technique. But it also leads to false patterns.