Nobles are a new alternate currency type expected to be added in the game in September 2014. The purpose of Nobles is to enable large money transactions, where the Platinum piece is not enough. They will be worth the equivalent of 100,000 platinum and Nobles will stack up to 20. They're intended primarily as a way for players to transfer larger amounts of money than the system can currently allow otherwise.
Details on Nobles may change before or after being added to the game. SOE is currently seeking player input on them. See this thread on the SOE forum for more information and to give feedback.