Spoilers:
That's a really good point. They do all seem kind of religous in a way. I don't really have any ideas for the mark, but I don't think that the red hood is Carlos, but I could be wrong, escpecially after that one "hallucination" when Carlos found Ben after he first got the medicine (I know it was said that it was a hallucination, but I feel like we can't be too sure if it was a hallucination or the real thing). This could certainly support Carlos being the red hood if it wasn't just a hallucination. I also feel like the whole blood in jars thing will somehow come into play. Like we might end up seeing someone with a suspicious amount of jars hidden somewhere or see them buying/carrying jars.
Semi off topic
Another thing that doesn't sit right with me is Dr. Hernandez's murder. I don't know what it is but I feel like she isn't really dead and could also be the red hood. I feel like she could be alive because of ben seeing her figure at the top of W.H. after her death. That and the fact that I think in the first nightmare that we see on the plane, the red hood seems to possibly have a beak ike Dr. Hernandez, not sure if that is a clue or just a random detail.
Then there's the whole thing after the Russel situation. I have no idea of what to make of it unless it was supposed to be a metaphor for something. Possibly Ben or Chris pushing Russel off of a metaphorical cliff representing the sudden ending of their frienship.