ah...by no means am I an expert-still learning myself--looks like a 'bag mark'-when one coin drops onto another causing a 'mark'. No 'D' I have ever seen looks like that. I think its pretty cool, but leaning on one foot at a 45 degree angle would think pmd---keep it who knows!!!!
I just had a look at the extra D using a 21 mm Hastings Triplet loupe at a 45 degree angle under a lamp it is raised and not sunken.
It could be a retained dropped element. What happens is grease and debris fill the incused letter on the die. Continual striking of coins compacts it to great hardness. When it falls away from the die and the next planchet is struck, it is embedded into the coin. Sometimes it will fall away on its own, but other times it remains embedded in the coin. Chris
I am not an expert but this sounds logical to me.You can see from the last photos that the extra D is near the height of the S above it,if this is pmd someone is really talented.
It is barely (!) raised above the surface of the field, and it is also about the same size as the "D" in IGWT, not the mintmark. I still think it might be a retained dropped element. Chris
I just googled drop letter element it is considered a rare error to make a long story short the falling letter will be inverted.http://numismaster.com/ta/numis/Article.jsp?ad=article&ArticleId=8899
Chris, I was the first to suggest it could be a dropped letter. But now the OP says the anomaly is raised which makes the possibility of a dropped letter less likely.
It is NOT raised. That extra D is not raised. I know the OP has the best opportunity to make that call, but I would bet my next paycheck that that extra D is in fact recessed. Compare the shadows and highlights to the other letters around it and they all are evidence that the extra D is sunken into the coin; they are on opposites sides of where they should be if it was raised. I would say that's a dropped letter, like Hobo suggested in post #5.