I very seldom encounter early U.S. stamps in the lots I tend to purchase and, when I do, I have to rely on the descriptions given in the Scott Standard. Those are reasonably good but in most cases lead to a fairly tentative identification.
I recently ran across the stamp illustrated below and because of the non-existent margin at the top my identification is really tenuous. For now, I am assuming it is Scott #15, Type III, but I would really appreciate a second opinion from someone who is more experienced than I am. The thing that is giving me some pause are the pearls engraved in the lower left (3? 2? 2 and a sloppy one).
