The Great Seal of the Realm is used to symbolize the reigning monarch’s seal of approval on important documents of state. In theory there is one per sovereign but another abdicating king, Edward VIII, who gave up the throne so he could marry Wallis Simpson, never had his own seal. On the other hand, Queen Victoria had to have four as they wore out.
There is a Duke Street that leads off Piccadilly; this was named as a compliment to James Stuart, who was the Duke of York before he was king. Benjamin Franklin used to stay at lodgings in a Duke Street off Oxford Circus, which may or may not have been named after James II; Franklin’s landlady was supposed to have enjoyed his company so much that she reduced his rent by over 50% to lure him to stay on.
Piccadilly itself takes its name from an item of clothing: In the 17th century a ‘pickadil’ was defined as “that round hem or several divisions set together about the skirt of a garment or other thing; also a kind of stiff collar, made in the fashion of a band”.