Emerald Tablet
In the German Netflix series "Dark" (2017), it symbolizes the caves' closed time loops with each loop being 33 years apart, with the past affecting the future and the future influencing the past. The Triquetra is of significant symbolic value to the time travelers. This symbol can be seen on the Cave's metal door, on the Emerald Tablet, in The Stranger's papers and in the Sic Mundus photo.