Question:
Brother,
This past weekend i was at a Catholic retreat where the Priest was giving a lecture on the various symbols that satanists use. He showed the "All-Seeing-Eye" within the triangle and said that it is a satanic symbol.
Ironically enough, i then went into the chapel and saw the symbol as one of the icons lining the altar. I asked him about it and he said that i bring up a good question as to its origins, he wasn't really sure and said that maybe some early Catholics didn't know the meaning of the symbol. I've seen it on a hat that Aleister Crowley wore in a famous picture of him.
Did the symbol originate with the Catholics and then Satanists steal it to pervert it? I can see where a triangle could represent the Trinity and the eye of God watching all. It just confuses me as to why Satanists would use the symbol as well as Catholics?
The priest also said that one time he put on a vestment and the vestment had an upside-down triangle with an eye on it, which confused him as well. Any help is appreciated very much. Thanks Brother.
Dear Matthew:
The "all-seeing-eye" does not have its origin in Satanism. The origins of this symbol goes way back to ancient Egyptian mythology as the Eye of Horus (an Egyptian god). It has also been used by the Buddhist.
The Buddhist were the first to associated the eye with a triangle symbolizing a trinity called the Triple Gem. These are things the Buddhist take refuge in and seek guidance. For them the trinity was Buddha (the enlightenment within man), the Dharma (the teaching), and the Sangha (the community). Interestingly enough this Buddhist trinity is similar to the Christian Trinity as Father (Buddha), Son (the logos / teaching), and Holy Spirit (the community).
In all cases that I know of the eye is a symbol of God in some fashion.
The symbol on the U.S. Dollar bill was placed there as a symbol of God looking down upon the American experiment with approval.
The eye in Freemasonry represents the all-seeing eye of God.
The all-seeing eye as we typically see it today first appeared somewhere around the 17th century. In modern depictions the triangle is specifically associated with the Christian concept of Trinity.
As for Satanist, the people in Satanism have borrowed all sorts of symbolism to pervert to their own purposes. Satanist also use the symbol of the Cross. Does this make the Cross satanic? If all a Satanist had to do is adopt a Christian symbol for themselves and thus we couldn't use it anymore because it is now "satanic", we would have no symbols left 
It is also claimed that the upside-down Cross is satanic. It is not. The upside-down Cross is actually the symbol of Peter who was crucified upside down.
One will find upside-down crosses in churches and even on some of the papal chairs. That is because it is the symbol of Peter and a symbol of humility, not of Satan.
Actually it is rarely Satanist who use the upside-down cross, but non-Satanists who interpret it as satanic. The reason for that was because non-Catholic Christian writers misinterpreted the symbol and presumed it was satanic. The misinterpretation caught on, even among Satanists today who may use it now that it has been given an anti-Christian meaning by Christians.
The downward pointed triangle is also not satanic. The downward pointed triangle refers to a Chalice (that contains the Blood of our Lord) and to water (water flows downward) implying the grace that comes of heaven. It may also stand for the womb (from which Christ was born).
I am sorry, but this priest really does not know what is talking about but is merely repeating urban legends.
God bless,
Bro. Ignatius Mary