In this Fallout Wikia page it mentions the grafitti referring too the DLC Honest Hearts. It says Where's New Canaan anyways? Well, If I remember right, Ringo says he's bringing his caravan up to New Canaan (my apologies if this topic has come up before I don't recall it though) Think this is a possiblity??

Honest Hearts DLC: http://fallout.wikia.com/wiki/Honest_Hearts

Yeah, I mentioned this in my speculation thread.

He's most likely the route for people to go to New Canaan. (Replaced by another NPC if the Courier kills him by helping the Powder Gangers.)

My apologies, I didn't even check out DLC section until they recognized the release a day or two ago for pc

Maybe a small role. Like an unmarked quest or something to help him get the branch started. Some other character would give it if he is dead/you never interact with him.

Well I killed him in my save files so I hope not. Or if he is I hope they put somebody in to take his place if he is dead.

Well, it's quite possible that he has nothing too do with the quest at all. You'd just figure that if you'll be in New Canaan and you DIDN'T kill Ringo, maybe he'll be there?