I don't think that graffiti is a crime, vandalism is. Creating a wall art is good and the artist is filling up walls in streets just to inspire. The vandalism is the crime because they ruin some private properties walls or structures, but if you're allowed to paint there as an art then it's not a crime
In most places, graffiti is considered illegal. Depending on the country or region, it may be considered vandalism, which is a type of criminal activity. In some cases, it may be considered a form of artistic expression, but it is still illegal in many places.
All states, as well as many municipalities, have laws that make it a crime to spray graffiti on public property or private property that you do not own or have permission to use. Graffiti crimes are very common offenses, especially in larger communities.