Like I said in my first post, crappy tags just suck, but there are some wicked street-artists out there. For you who just discard it as trash, you should check out
this guy's art.
Not only is it well made, it is also often strategically put to be very provocative.
For example
This was painted in a slum in Bethlehem 2005.
And this was drawn on the Israeli West Bank Barrier the same year. (Enlarge to see what it says)
This guy is good enough so that a number of his drawings have been deemed so good, and "important"(Can't find a better word atm) to be allowed to remain.