Graffiti has been found in very old cities. For example, in the Roman Empire, people wrote messages and drew caricatures on walls. Graffiti is also found in many places. Some of people do murals of graffiti rather than just writing one mark in a location. It was used for good instead of vandalism. Probably the simplest graffiti is when a person cuts (or carves) the name of a lover on a tree with a knife.
Today, many graffiti are very complicated mixtures of writing and pictures. They are sometimes made by gangs and applied with spray-paint to buildings, bridges, street signs, and other areas. These are often signed with a tag (in graffiti slang, a signature), which is a shape special to an artist or group.