1933 Saint-Gaudens Double Eagle ($20 gold coin).
These are the last of the long series of U.S. gold coins produced in various
denominations since 1792. Over 400,000 of these were struck during the
first quarter of 1933, but none were released into circulation. All were
supposed to have been melted down except for two reserved for the Smithsonian
Institution. Today
three are known to exist.