It's turgid academic prose and I doubt that it communicates clearly, even to an academic in the field. But perhaps it does, if the phrases are actually technical terms with clear meanings. This is what I THINK it means. A piece of graffiti sends two messages. 1) This is my territory, my land, my neighborhood, my part of the city. 2) This is my wall, my building, my playground, my bridge, my subway car. (1) is the "non-specific territorial message," (2) is the "claim to the built environment."

The text reads as if its source was an academic journal, or at least something more advanced than you would typically find on an everyday basis. That said, I'm going to say that 2 is correct. My reasons are that graffiti typically claims a section of wall as belonging to the artist (in an art sense, not a legal one of course). Therefore the wall could be counted as the territory of the artist. The graffiti is likely to be a unique piece and therefore does not lay claim to a section of a city in the way that gang-sign graffiti would, the latter then would be specific to territories. Because the sentence starts with "So, ..." I'm guessing there is at least 1 preceding paragraph that may give more insight if a more accurate meaning is required.