I have noticed some lately. They are set up, over 7 feet tall and have long cords, which are thrown over wires.
After workers left, the cords were moving.
Someone probably has the answer
When installing new electric, fiber, telco cables on poles, the workers often install a series of temporary guide pulleys on each pole along the route, threaded with heavy ropes all leading back to a trailer with huge spools of the final cable - then go to the other end and pull carefully until the new cable is in place, whereupon it gets lashed in final position and the pulleys are taken down for the next job. There was probably someone near the spools keeping an eye on things even if most of the workers were at the other end of the rope…
Thanks!