For those of you who haven't yet heard, the sign over the gates of Auschwitz, the Polish concentration camp, which read "Arbeit Macht Frei" (work will set you free), has been stolen. Experts believe that this was a pre-planned theft to commission by someone who collects Nazi memorabilia. Certainly, it's not something that could be sold on the open market. If the deal fell through, the sign might be melted down, and this would be a real tragedy, as it is the materiality of Auschwitz that gives it its power. The article I have linked to explains it well - I agree that this is one instance where a reproduction would fail to be an adequate replacement.