Graffiti can be a minor detail that is barely noticed in a fictional world, or it can act as an important system of communication for those that know the symbols. Either way, graffiti tells a story and including it can act both to age your world as well as make an impact. Graffiti is often rebellious in nature, so from it one may learn who or what is despised, or you may learn a few new curse words. Different artists or groups of peoples may have distinct styles. Graffiti can be used as a form of protest, to mark territory, to intimidate, or to inspire. It may have been placed to mark gang territories, or to advertise illegal wares being sold nearby.