If you see graffito on overpasses, train box containers, signs, brick walls or streets, this is considered littering because someone has defaced public property. During the Great American Clean Up, groups will be painting over many defaced spots.
Much of the graffito I’ve seen (not this to the left) show good artistic talent. I wish that the talent could be used to paint murals in unsightly areas of the city. The railroad overpass by the Nashville Zoo at Grassmere has nice murals painted on the columns. The murals depict some of the animals at the zoo. Thankfully, no one has tagged this artwork.