Graffiti in ancient Rome was often very political, and if it attacked powerful families, they would act quickly to erase it and punish those who wrote it, if they could be found. In Suetonius (I believe), you can find the story of Brutus entering the Senate to find his seat tagged with references to his ancestor, the first Brutus, who drove out the last king of Rome. This perhaps, among other things, compelled him to turn against Julius Caesar.