If one does not agree that grafitti is of an artistic nature or has political involvement I highly recommend one watches STYLE WARS the film goes into depth how the grafitti culture of the late seventies in new york was expressing the same socio political issues of the time as hip hop was as well. Also check your bookshops about it is a fascianting subject.

The link for this is "http://www.amazon.com/Style-Wars-Sam-Schacht
/dp/B000A7DVZO/ref=pd_bbs_sr_1/
102-6533293-4382533?ie=UTF8&s=dvd&qid=
1187145506&sr=1-1

Subway Art - http://www.amazon.com/Subway-Art-Martha-Cooper/
dp/0805006788/ref=pd_sim_d_3/
102-6533293-4382533?ie=UTF8&qid=
1187145506&sr=1-1 is also a great book.