The word on the street is that this was the work of the same jerks who busted out the windows at quietstormpgh a few nights back.
The graffiti they left here, in addition to your standard issue circle A anarchy symbol, said something along the lines of "There are no good corporations: Stop [illegible] buying ..." In my personal opinion, it comes off less as black bloc and more as wannabe -- more as something somebody would do if they wanted to see the anarchists get blamed for it. I suppose I could be wrong, but to me this screams either bored teenagers or CIA bullshit.
And thanks to pghwob for providing me with this bizarre little link.
Also, I ranted about this all in the pittsburgh community. Check out my rant -- I use the word "bougie."