Triquetra
The Triquetra is a knot-like formation with three ends, commonly shown interlaced around a circle. The symbol is also known as the symbol of charm, and is used in the depiction of several Norse and Scandinavian items such as the Mjölnir.
The Triquetra was heavily used by Norse pagans, as they used articles like pendants resembling the Mjölnir with a Triquetra symbol crafted on it.