Shutting down the New York City subway in advance of superstorm Sandy helped avoid catastrophic damage to the city's most vital transit system. But it spelled disaster for one of the subway's quirkiest and most beloved works of art.

Sometime after the subway shutdown last October, vandals broke into and defaced Bill Brand's "Masstransiscope," the nearly 33-year-old art installation that sits on an abandoned Brooklyn subway station platform in the darkness, visible to those B and Q train riders who know to look out...