A cross composed of four interlaced triquetras -- this is called a "Carolingian Cross" by Rudolf Koch.
See Image:DSCN0076ConstantineWarMemorial.jpg for a form of this on a Celtic cross.

Since the Triquetra is a Trinitarian symbol, this cross could be considered to be an emblem of the Christian Trinity. For other Trinity crosses, see Image:Cross-Bottony-Heraldry.svg , Image:Borromean-cross.png / Image:Borromean-cross.svg , Image:Celtic-Cross-Vodicka-decorative-triquetras-red.svg , and perhaps Image:Cross-Flory-Heraldry.svg .
own work (Vector graphic) based on Image:Triquetra-Cross.png
first-uploaded version by Gothika, second-uploaded version by AnonMoos