Triquetra interlaced with a circle (ribbons or pseudo-Celtic knotwork).
This is a traditional Christian Trinitarian symbol, but similar signs are also sometimes used by new agers or neo-pagans (though more often in non-interlaced form, as in Image:Zoso.svg, File:Triquetra on book cover.jpg, or File:Triquetra.jpg). In this interlaced form, can be known as the "Trinity knot".

(Christian Symbolism: The Triquetra represents the Holy Trinity: the Father, Son, and Holy Spirit. The unbroken circle represents eternity. The interwoven nature of the symbol denotes the indivisibility and equality of the Holy Trinity. It symbolizes that the Holy Trinity is three beings of power, honor, and glory but is indivisibly one God.)
Own work
Eugenio Hansen, OFS