According to this Wikipedia entry: "A clubbed thumb is a term used to describe the genetic clubbing of one or both thumbs. It is characterized by a particularly short thumb that is round in section and bulbous at the end. The thumb nail is very wide and short. The scientific term for clubbed thumb is Brachydactyly type D or "BDD". Clubbed thumbs are historically thought of as a sign of royalty. This rare condition was much more common in royal European blood-lines than in the general population and was used as a factor in determining the pureness of the blood."
In all their greatness:
This blog entry goes out to my lady, Rayne, who shares in my newfound royalty! Though I'm still more royal than her because both of my thumbs are clubbed, and she's only got one.