Why is there so much grafitti (art) in hispanic neighborhoods? can't they afford sketch pads?

Firstly, it isn't because it is an hispanic neighborhoods. It happens mostly in the inner city where there is less surveillance, many suburban kids generally go the inner city to tag walls and trains as well as others and they can also be found wherever their is high gang activity. Tagging is not a "race", "ethnicity", "poor", or "minority" thing, it's an artistic counter and sub culture. It is art, whether or not you like it and many do draw in sketch pads, but sometimes, the destruction of public property specifically with a specific drawing communicates the social and/or political message the artist is trying to get across. Sometimes, it's the only way to get people's attention, especially if you are from a group or culture or opinion that is often overlooked and/or not taken seriously.