Numbers stations go back as far as World War I. During the Cold War, there were hundreds of secret broadcasts. Intelligence agencies sometimes started a transmission with a bit of music (one UK station was dubbed the "Lincolnshire Poacher" because it began with a few notes from an English folk song), then recited the code five numbers at a time. Operatives with the key listened and transcribed top secret messages. By the '70s, regular folks were picking up the frequencies on ham radios