how do you know it's specifically a gang tag?

If you are in any type of group causing crime, it's a gang. Simply put.

City of Oakland Public Works Agency referred this issue to CALTRANS MAINTENANCE, service request # 470828. Please contact that agency to follow-up. For more information, please visit the "Helpful Links to Other Resource Partners" at the link below.
http://www2.oaklandnet.com/Government/o/PWA/Connect/ReportaProblem/index.htm
Thank you.

gone, thanks.

Thanks for fixing this issue!