To anyone doubting the "antitrinity"
First, definitions....lets be a little more specific: Trinity refers to any grouping of three, thus the three pens I have on my desk are a trinity. The Father, Son and Spirit are Triune...Three in one Tri=3, Une= one. That being defined, there is an opposing trinity referred to in Revelation. The Dragon...chapter 12, identified as Satan. The Beast from the Sea, who had a mortal wound that was healed...that's the Antichrist, thats ch.13, and in the latter half of Chap.13 is the Beast from the Earth, who is given power to perform miracles on the behalf of the first beast to make the inhabitants of the earth worship him, commonly referred to as the False Prophet. A group of three, opposing God, thus a trinity.
Now, as far as Greys avatar, that is a Triquetra, originally used as filler artwork, later used to represent, you guessed it...the Triune nature of God.It has been adopted by multiple belief systems in centuries past, but now it has been usurped by Christians. It bears a simplified resemblance to a rounded version of the Scutum Fidei, or Shield of the Trinity, which is probably why it has been grabbed and used.