Unless the sunlight catches them just right they are invisible from the ground. They zig-zag along the tops of the light poles on either side of Avenue A. It looks like mono filament to me. What possible use can they have? At points, like in this photo, the zig-zag is continued by thicker, more apparent rope. Neither would be capable of carrying electric current, and the mono-filament would not be strong enough to act as a guy wire. It’s a mystery.