This retaining wall has been regularly tagged since 1979. Though technically illegal, the wall has become an institution of sorts. City officials even placed trash cans along the wall to discourage littering. People call the 1,120-foot wall the “Community Bulletin Board.” Artists post all kinds of things from victory announcements and personal victories to activism slogans and tributes. Most of the art is done by students and local residents, but sometimes, a professional contributes to the piece. Local historians believe there are at least 250 layers of paint in some…