Multiple realities
(covers information from several alternate timelines)

A quantum signature was the unique signature with which all matter in a universe resonated. It could not be changed by any known process, and was considered to be the basic foundation of existence. However, the quantum signature did differ between different quantum universes, such as between the prime universe and the mirror universe. (TNG: "Parallels"; DIS: "Despite Yourself")

During the first Federation-Klingon War, the USS Discovery found itself transported to the mirror universe due to an incident with its spore drive. It quickly detected that the quantum signature of other ships were inconsistent with its own, helping them determine that they had left their universe. Michael Burnham later used the quantum variance of a Starfleet insignia to prove her origins to Emperor Georgiou. Georgiou confirmed this inference with a scan of the metal insignia. (DIS: "Despite Yourself", "Vaulting Ambition")

In 2370, Lieutenant Worf was thrown into a state of quantum flux as a result of an encounter with a quantum fissure, causing him to shift between different quantum realities. Detecting this flux in Worf's cellular RNA, which extended to the subatomic level, Lieutenant Commander Data was able to determine that Worf's quantum signature was not consistent with the resonance of matter in the rest of the universe, and that he had originated from a different quantum universe. (TNG: "Parallels")

See alsoEdit