Symbols of Rome; the Madonna, a scooter and graffiti.
Scribbling emotions on walls has been a tradition in Rome going back thousands of years and even the word "graffiti" was first used for markings found in the ruins of Pompeii.
While there are a few interesting works of street art to be found most are an eyesore. On the shops. On the subway cars. Even on the churches. Everywhere within about a 2 meter radius from the ground, anywhere there's a nice "canvas" of wall, seems to be fair game.
Practically, it can't be good for the old buildings. Cleaning it up, meanwhile, is frustrating and expensive: Repainting a 4-story palazzo can set you back €40,000.