I know that graffiti is usually criminal activity. However, Graffiti can also be legal.  I think the style is beatiful and makes the city better, however I only participate if it is legal.  Here is a picture I made.  It is in the graffiti style, but it is a silkscreen print.  I made it in my university art class.  I will bring a copy to class for you to see! Here is a great Art dictionary if you need specific Art vocab.

Also look at this amazing piece of 3-D street art being created!