It seems that there are numerous possible explanations, ranging from the existence of a nearby drug dealing centre through to a way of marking a gang's turf. Is it a coincidence that the power line is close to a newly-opened coffee shop? Is there something going on in our vicinity that we're not aware of?
However, I'm hopeful that the explanation is more benign, perhaps the outcome of some adolescent rowdiness!
(edited 11 Sept)