So-Called Dollars are a category of commemorative coins that were not issued as part of the official U.S. currency but celebrate specific events, people, or places. The term "So-Called Dollar" refers chiefly to pieces that are the same size as an official U.S. dollar coin and often were produced in conjunction with expositions or special occasions. The Hibler and Kappen reference is a cataloging system used to classify these tokens and medals. In 1939, several So-Called Dollars were issued to commemorate the 1939 New York World's Fair, which became a notable event in numismatic history.