Someone usually knows who the John and Mary are in John + Mary forever, so this would be a chance to share that information or defend against accusation, online.
Today walking through the forest I saw an awesome old long graffiti on a tree in a national park with misspelled words and everything. It reminded me of the time I incised into the wet cement of a sidewalk on my way home from school, "The Gratful Dead".
I think there already are general graffiti databases but this one would be just for trees and would be an opportunity to share info on some of those a really old tree graffitis.-- JesusHChrist, Feb 07 2016random, halfbakery