Cross of Triquetras or the Carolingian Cross. This symbol is used by Christians as a symbol of the Trinity (Father, Son and Holy Spirit). This appropriation is particularly easy because the triquetra conveniently incorporated three shapes that can be interpreted as Christian Ιχθυς symbols.
A common representation of the symbol is with a circle that goes through the three interconnected loops of the Triquetra. The circle emphasizes the unity of the whole combination of the three elements.