Eye of Providence

"A Christian [Trinitarian] version of the Eye of Providence, emphasizing the triangle representing the Trinity."
http://en.wikipedia.org/wiki/Eye_of_Providence

The Eye must represent God as a united entity, the three sides representing the three persons of God: the Father, the Son in Hypostatic Union with his Human and Divine natures, and the Holy Ghost/Spirit.

The doctrine of the Trinity teaches "the unity of Father, Son, and Holy Spirit as three persons in one Godhead."
http://www.britannica.com/EBchecked/topic/605512/Trinity

This Trinity Triangle Eye has been used in art as well. See the above Wikipedia article.