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I know nothing about the area or the graffiti, so any observation of mine is just a guess. Graffiti can be thought of as puerile defacement, which is indeed sad. Something like gang-related graffiti would seem very sad and troubling to me. What the "artist" thought, I don't know, but it's entirely possible that it was an expression of pride, or community, or individuality, or daring, or even hope.
Whether the photo fits the "street" genre isn't of interest to me. The scene made enough of an impression on you to take the picture, and it's elicited a response from at least one viewer.
