This style almost seems like it is statement or a logo of expression. Are they appearing on every building or every other building? I wonder if the artists need governmental approval before attaching the "art" to the building and if he or she needs to pay a fee..... hmm this is very interesting @leaky20. Thank you for sharing this.
Not every building just ones that speak to the artist I suppose. And no they do not have approval to do this. Its basically illegal in the same way that conventional spray painted graffiti is. They usually do it in secret, at night and while wearing a mask. A lot of street art gets taken down by the city or individual people and many artists like Invader have been arested.