There are plenty of links you can draw if you have a mind to do so. The actual meaning behind graffiti is so highly distorted, on purpose, that it means me wonder what a lot of it actually stands for. Bathroom stall messages tend to be a little more straightfoward I find it interesting where you don't see bathroom stall engravings though. You'd think airport bathrooms, where all of humanity takes a seat, would have them everywhere. But they don't at most airports. Maybe because they're rigorously maintained. Or because people traveling don't have the time to be expressive. Or because there's simply too many people around for being mischievous. Or maybe because bathroom graffiti is largely done by people who use the same bathroom often. (As is the case with Truck Stops and Bars.)
Ironically I remember a bathroom at this one bar in Germany that was covered, wall to wall every surface except the toilets and sinks, in graffiti. Just to bring this post full circle.
I have seen genitalia pics, "for a good time call" "call this person for a good time", gang sign, magical symbolism, poetry, attempts to curse the reader with bowel trouble, "I exist", "they exist", "we exist" (I haven't seen anybody say nothing exists), "[outgroup/person] is [negative trait or behavior, as seen by the writer] and [commits disgusting and evil deeds, as seen by the writer]".
I find it interesting where you don't see bathroom stall engravings though. You'd think airport bathrooms, where all of humanity takes a seat, would have them everywhere. But they don't at most airports. Maybe because they're rigorously maintained. Or because people traveling don't have the time to be expressive. Or because there's simply too many people around for being mischievous. Or maybe because bathroom graffiti is largely done by people who use the same bathroom often. (As is the case with Truck Stops and Bars.)
Maintenance does seem to play a large part, as well as the tools available to the writers.