Just because the 'he is mar' clue bugs me, I make my last theory on this site.

There is no bar on the 'H' and to me it looks like 'II is many'. If you've been stabbed, bleeding out you don't have the energy to write a sentence. A name would suffice. Why else would you scrawl on a wall in blood?! Obviously to alert people. But if another man came to the scene, maybe that is what he was trying to tell them. I don't see multiple red johns, but maybe a master/apprentice variation.

I'm 99.9% certain all the fans will see a new episode ending tonight. Thank you all for the theories. It's been fun!