Is an eruv a sign?

No. An eruv is a purely functional device that encloses an area, and as opposed to signs, eruvin do not have an expressive component. In fact, many attachments are virtually impossible to spot.

Many times, an eruv may be paired with a sign because even adherents can’t tell where they are:

In this photo, one of the rubber tubes is an eruv lechi while the other is a utility attachment:

Court have reached this conclusion several times.

The US Court of Appeals for the Third Circuit (which is binding on Federal Courts in NJ) said:

“[W]e conclude that the plaintiffs have not met their burden of showing that affixing lechis to utility poles is “sufficiently imbued with elements of communication” to be deemed expressive conduct… on the record before us, it appears that the eruv serves a purely functional, non-communicative purpose indistinguishable, for free speech purposes, from that of a fence surrounding a yard or a wall surrounding a building.” (emphasis addded)

In fact, the Court went so far as to say why this is not a serious claim:

“[T]here is no evidence that Orthodox Jews intend or understand the eruv to communicate any idea or message. Rather, the evidence shows that the eruv–like a fence around a house or the walls forming a synagogue–serves the purely functional purpose of delineating an area within which certain activities are permitted.

We also reject the plaintiffs’ contention that the eruv may be deemed expressive simply because some residents of Tenafly who are not Orthodox Jews discern various unintended messages emanating from it, notwithstanding that these persons would not be intended recipients even if the lechis were meant to send a message. To accept this position would mean that whether conduct is expressive depends entirely on how observers perceive it–even if the actor had no communicative intent, and even if the actor disapproves of the message (or messages) discerned by the observers.” (emphasis added)