Last week on the day I took shots of this symbolic fence (the thin [nylon?] wires in the photos) along 6th Avenue just below 23rd Street I couldn't find anything on line confirming that it represented a currently-valid eruv, or shituf mevo'ot [sharing of the alleyways], but the concept itself fascinates me.
it is what you suspect.
There is now a big deal, they want to put one up in the hamptons and the residents there are fighting it not sure why.