The all seeing eye is one of the most popular ones. Triangle.
It is a symbol showing that there is a greater being (the big man upstairs) that is the ultimate judge, that you are minuscule to. So, it is not "satanic" at all.
It's pretty cool to think about, so I can see why you would use it on an album cover, etc. Since people share their love for the symbols and mystery, it becomes even more popular and shares the idea.
So, the new "pop" celebrities want to jump on this boat since they like fame and so they adopt it. Doing so attracts some people to them and shares the idea even more.
I Like some of the symbols and mystery behind them greatly, but with how much they have become popular, and the changes pop does to things, I wish to find a new subject.