Not necessarily. Federal Courts governing New Jersey have ruled that an Eruv is not in the same legal category as objects, such as crosses or menorahs, that express a religious message.
This issue came up most recently in the opinion the Third Circuit Court of Appeals (which governs New Jersey) decided in the Tenafly litigation.
In that opinion, the Court said that the claim an eruv is expressive (like the 18-foot Chanukah menorah at issue in Allegheny County v. Greater Pittsburgh ACLU) was misplaced.
While the Court did agree that "things ordinarily used for functional purposes can be used for communicative purposes as well", they went on to say:
"the 18-foot menorah was both intended and understood to express "a recognition that Christmas is not the only traditional way of observing the winter-holiday season" and "an acknowledgment of Chanukah as a contemporaneous alternative tradition.""
"In sharp contrast here, there 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." (link to opinion)
Just as someone cannot look at PVC piping used for electrical or other purposes on a home and claim it is a sign, one may not change the ordinary way PVC piping is construed based on their subjective impressions.