By Ella Morton, Atlas Obscura
In early 1942, the United States government began issuing a special set of banknotes custom-made for just one of the 50 states: Hawaii. The back of each note looked identical to the existing U.S. paper currency apart from one major difference: the word "HAWAII" was stamped across it.
The design of these notes wasn't the most elegant—the "HAWAII" looked as though it was inscribed by someone with a black ballpoint pen and a ruler. But that's understandable, given their circumstances: these banknotes were an emergency series, rushed to print in the months following Japan's attack on Pearl Harbor. The idea was that if Japan invaded Hawaii, the U.S. government could immediately identify and devalue the state's currency so it would be worthless to the Japanese.
"The Federal Reserve notes were issued in the San Francisco Federal Reserve District, which included Hawaii in its jurisdiction," says Mark Anderson, Numismatic Consultant to the Museum of American Finance. If the need had arisen, "the notes' distinctive features would have allowed prompt and easy identification." In addition to the big HAWAII stamp, each note featured brown treasury seals instead of the usual blue or green, and had "Hawaii" printed vertically in small black block letters on the front...