Well, I've been following the thread from the beginning, and I've conclusively determined that I stink at this. For this one, I knew it was a point I'd examined myself many times, and I still had to dredge through a bunch of types before I found it. (Liberty nickel? Barber dime? Merc?) I figured my only chance was to get in when not many other folks were looking, and when I had some undivided attention to apply. No need for a specific date or mint on this one: