Equating him to a graffiti artist would be a bit much given with what we have. He put his logo on some dingy brick building near some alleyways. When he starts tagging every other public building, then I'll pull out the pitchforks.
As is, it is much ado about nothing significant. A high school loner who knows how to draw and decides to celebrate on some run-down piece of property when he's at an emotional high... seems pretty in line of a Parker thing to do. Lest we forget, the kid turns into a vigilante and concocts an arachnid masked identity, as a self-appointed protector of the city. Comparatively speaking, which is the more "out there" behavior for his personality?