The Hawaii overprint notes, an emergency issue of U.S. currency overprinted with the word Hawaii, became the only bills allowed to be used there following the attack on Pearl Harbor. Any money captured by the Japanese if they invaded Hawaii could then be easily distinguished. The bills were introduced on June 25, 1942, and withdrawn effective April 1946; many were destroyed.
Shown here is a $10 Federal Reserve Note, of which 10,424,000 were printed. This bill is scanned from the collections of the National Numismatic Collection at the Smithsonian Institution.
Banknote: Bureau of Engraving and Printing (image courtesy of the Smithsonian Institution)