Graffiti may also express underlying social and political messages and a whole genre of artistic expression is based upon spray paint graffiti styles. Within hip hop culture, graffiti have evolved alongside hip hop music, b-boying, and other elements. Unrelated to hip-hop graffiti, gangs use their own form of graffiti to mark territory or to serve as an indicator of gang-related activities.[from wikipedia]

Both its artistic and destructive forms.

Graffiti found around the Lake Merritt area and Chinatown.

In modern times, paint (particularly spray paint) and marker pens have become the most commonly used graffiti materials. In most countries, marking or painting property without the property owner's permission is considered defacement and vandalism, which is a punishable crime.[from wikipeia]

Done using flow pen on the arch supports of the pedestrian bridge across therailroad tracks by the Amtrak Station.

Art and damage found all around the town.

The cliffs opposite the dock were covered in graffiti left by years of ships docking there.

Graffiti found on the walls of an underpass that went under the train tracks.