Check out the new way the city is combating graff to appease the likes of faggy night club owners and such.
http://miami.cbslocal.com/2011/05/11/miami-using-high-tech-way-to-battle-graffiti/
They want to keep the device top secret, but here's how it probably looks.
http://www.campussafetymagazine.com/Channel/Security-Technology/Products/2008/11/Graffiti-Sensor-Recognizes-Aerosol-Fingerprint.aspx
TELL YOUR FRIENDS.