Inverted "S" mintmarks are known for several year/denominations from the mid- to late-1940's, especially on the Mercury dimes. I spend a lot of time looking for them, and have been reasonably successful (still no cent though). I was checking through some scrap silver quarters for varieties and came across a 1942 quarter that appears to have an inverted straight serif "S" (per CONECA). I have included a couple of pictures below. The first is the correct orientation, the second is the same picture flipped upside down. To me the first look inverted and the second looks correct. If you have compare this to the 1942 dime with the inverted straight serif "S", they look very much the same. Let me know what you think TIA for any insights.
It is at times frustrating with slow responses or sometimes none. I am not familiar with these and I am still pretty much new. Did you by any chance do a side by side comparison with a normal one online?
As to what I think may not matter, but I think the one on the right looks correct. I would also be doing the same as you, asking the experts here, sorry. Good luck.
