I recommend you do some research about Os Gêmeos.
They are brothers, born in SP about 30 yrs ago who became internationally acknowledged by their fantastic art. A young talented guy I have the pleasure of meeting in person is Gabriel Rao. Yes, São Paulo is interesting concerning this.
When you visit Pinheiros/Vila Madalena during the day pay close attention to the graffitti on tiles in the walls of Cemitério São Paulo. The curious things are some works based on death and after death life. Unfortunately more than half of them are just "signatures" of some urban "gangs", IMHO.
I grew up in NYC and remember hearing so many negatives about graffiti, as it was always called back then. Over the years it became known as art and in many cases, the term is justified. The gang symbols or kids with a spray can kind of defacement holds no artistic value with me, but there are some very remarkable and talented artists out there whose work takes careful planning and in many cases local government approval.
So - I'm enjoying some of what I see here to answer your question.