Project Sign

American UFO panel

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Last updated

July 17, 2026

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Project Sign was a classified United States Air Force program that ran from December 1947 to February 1949. Its primary goal was to investigate sightings of unidentified flying objects (UFOs) and determine if they originated from extraterrestrial sources or posed a threat to national security, particularly from the Soviet Union. Project Sign investigated 243 sightings, with some researchers initially suspecting advanced Soviet aircraft, while a minority considered the extraterrestrial hypothesis. The project was later scaled down and evolved into Project Grudge, and then Project Blue Book, which continued until 1969. No physical evidence of extraterrestrial origin was collected during these investigations.12

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Project Blue Book
The first was Project Sign, a classified program that tried to explain a number of military-reported UFO sightings and determine whether they were extraterrestrial in origin, while also considering potential threats to national security, especially those related to possible espionage by the Soviet Union. Project Sign lasted from…
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The first was Project Sign, a classified program that tried to explain a number of military-reported UFO sightings and determine whether they were extraterrestrial in origin, while also considering potential threats to national security, especially those related to possible espionage by the Soviet Union. Project Sign lasted from…
Read More

unidentified flying object
Flying saucers and Project Blue Book
…an investigation of these reports, Project Sign. The initial opinion of those involved with the project was that the UFOs were most likely sophisticated Soviet aircraft, although some researchers suggested that they might be spacecraft from other worlds, the so-called extraterrestrial hypothesis (ETH). Within a year, Project Sign was succeeded…
Read More
…an investigation of these reports, Project Sign. The initial opinion of those involved with the project was that the UFOs were most likely sophisticated Soviet aircraft, although some researchers suggested that they might be spacecraft from other worlds, the so-called extraterrestrial hypothesis (ETH). Within a year, Project Sign was succeeded…
Read More