(covers information from several alternate timelines)
A temporal signature is a detectable phenomenon which defines an object's position in time.
In 2372, a power surge from the USS Defiant's warp core knocked Captain Benjamin Sisko's temporal signature out of phase, pulling him into subspace. While in subspace, Sisko did not experience the passage of time, reappearing to his son Jake at different intervals in Jake's lifetime, due to a subspace link which had been created between the two of them because of their physical proximity during the initial accident. The timeline in which these events occurred was negated in 2450, when Jake committed suicide, thereby severing the link and sending Captain Sisko back in time to the moment of the initial accident, where he was able to change history by dodging the energy discharge from the warp core. (DS9: "The Visitor")