[SPOILER WARNING]
Alrighty then!
So I think there are four images in total that contain these messages. It's certainly possible I missed some though! Anyway, I believe the mystery grave says something like: "Rest in pain, forever missing" (I was expecting there to be a name on the grave, it's kind of interesting that Mary calls this person a "they" and Reginald calls them a "him", though, is that intentional?).
After the argument with Twyla, when Mary hides behind a trashcan in an alley. I think the graffiti says something like: "Silly girl".
When Mary runs away from Reginald in his apartment complex, I believe the tags on the doors say "Run".
And lastly, I dont really know what the word in the creepy manga is supposed to be. My closest guess would probably be "Wised", but I'm not so sure. Maybe it's a name?