Project Sign was a secret initiative launched by the United States Air Force in 1948 to investigate unidentified flying objects (UFOs). The project aimed to collect and analyze reports of UFO sightings, particularly those that could not be easily explained. It was one of the first formal efforts by the military to study the phenomenon and assess any potential threats to national security. The project operated until 1949, when it was replaced by Project Grudge. Although Project Sign gathered various reports and data, it faced challenges in establishing conclusive evidence regarding the nature of UFOs. Ultimately, the project contributed to the ongoing interest and debate surrounding unidentified aerial phenomena.