Photographs from the Korean War often show captured American soldiers pointing the middle finger at the photographer.
North Korea used images of prisoners of war as a propaganda tool. The pictures were supposed to raise the spirit of the Korean people who fought against the overseas invaders. But cunning American soldiers, taking pictures, now and then put their middle finger in front of the camera.
The Koreans were not familiar with this indecent gesture, so they did not suspect anything for a long time. When the Korean military noticed that the prisoners in all the photos showed the same gesture, they asked what it meant. The Yankees replied that this is a gesture that means good luck in Hawaii.