It seems that a sigil is, most commonly considered, a symbol used in magic. That sets off a loud warning signal in my spirituality, one I don’t want to ignore.
According to several passages in the Bible (Jeremiah 23:13-24; Deuteronomy 13:1-5; 2 Peter 2:1), God had no love for false prophets because they were directly and harmfully affecting the people He created and loved.
I believe, looking at your question, that you are asking who might be the cultural leader of Christians, rather than strictly who is a leader on paper.
My thoughts about the two statements, "I believe in God" and "I know that God exists," could be summed up by two words, ‘ambiguous’ for the first declaration, and ‘apprehension’ for the second.
I can tell you what the text in the Bible says about hell, but that text has been so heavily debated and influenced by cultural ideas (such as Dante's 'Divine Comedy') that to me, it often feels like one needs an advanced degree in religious studies to sort it out.