Postcards with stamps and special cancellations.
Flag postcards;mapcards and aerial views.
Island Postcards and exotic places.
The self-declaration of "Principality" in 2006 is out of law.The title of "Prince" was officially given from the chief of the Holy Roman Empire (800-1806). Since the Holy Roman Empire nowadays doesn't exist any more, there cannot be new Principalities except Luxembourg, Liechtenstein and Monaco.Best wishes.