The Triquetra that appears on the cover of the Unknown's journal and throughout the series foreshadows multiple revelations as the series goes on. In the first and second seasons, it implies a relationship between the three major timelines (1953, 1986 and 2019). In the final season - that deals with two interrelated separate worlds - it implies the existence of a third world. Of course, the viewer only learns the existence of the third world in the final episode. That third world being the Origin world.

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