For the thousands of students who visit Auschwitz-Birkenau every year with the Holocaust Educational Trust, approaching the gates and setting eyes on those infamous words, "Arbeit macht frei", is invariably a moment of solemn reflection. The wrought iron sign has become a symbol of evil, grim shorthand for the sadism of the camp. Yet the sign is a replica, because two years ago this week the original was stolen to order. It was recovered but, for security and to avoid further damage, it has not been re-hung.
That crime naturally prompted both disgust and bewilderment. Perhaps we should not have been surprised, given that the theft took place against the backdrop of a thriving market in Nazi-era items. Last month, the press reported on the sale of Hitler's monogrammed bed linen, while, last week, a brass desk-set apparently made for him was auctioned in New York for a staggering £272,000.
Other items sold recently include a selection of rather dull postcards penned by Himmler, and Goebbels's school diary. Much of this material is mundane and of limited historical value, aside perhaps from representing what Hannah Arendt dubbed "the banality of evil".
The market in items associated with high-ranking Nazi officials is in highly dubious taste, as is the sale of real or replica SS uniforms for "fancy dress". But other items that can be bought freely are nothing short of appalling, from yellow stars designed to identify and humiliate Jews, to arm-bands worn by gay people imprisoned in the camps, or identity papers and uniforms from Auschwitz.
These are more than merely tasteless mementoes of a despicable regime, they are material evidence of the Holocaust. Collecting odd militaria is one thing, but it's difficult to comprehend how anyone - other than a museum - could think it appropriate to acquire items associated with the largest mass-murder of civilians in history.
Perhaps the most disturbing example was the Montreal shop offering punters soap made from the human fat of Holocaust victims. Its providence is disputed but, regardless, that someone would seek to profit from something so foul is outrageous. Why would anyone want to purchase an item believing it to be a grisly by-product of murder? The distress such sales must cause to survivors is unimaginable, as is the disrespect it shows to victims.
There is serious debate to be had over the place that Nazi-era items should have in our society. In Germany, where sensitivity is understandably high, they cannot by law be sold except to buyers who will display them in an appropriate educational context. Last year's ground-breaking exhibition in Berlin about Hitler demonstrated the power that physical objects from that time still hold; items Hitler had actually touched were rejected for fear of "encouraging a Führer cult". Clearly, Nazi memorabilia continues to have powerful resonance, and, given its relatively plentiful availability, we need to start talking about how to deal with it. Unlike in France, Austria and Poland, the sale of this material is not banned in the UK, but we should review whether some level of regulation is necessary.
As well as investigating the viability of legal restrictions on the sale of such items, we need to ask pressing questions both about those who profit from their sale and the "private collectors" who fuel the trade. Some may have a legitimate if misguided historical interest, but trading in Nazi memorabilia and items associated with the Holocaust also frequently takes place on far-right and antisemitic online forums.
There is also a danger that fascination with these objects, be it cultish obsession with the Nazi aesthetic or ghoulish fascination with Holocaust relics, distracts from the humanity of the victims of Hitler's regime. These objects represent the world as the perpetrators of genocide would have it. Often they tell us nothing of the lives that victims experienced before the Holocaust or the futures that were stolen from them.
It is important for young people to hear the testimony of survivors. The HET also believes they should have the opportunity to see tangible evidence of the Holocaust with their own eyes.
When displayed with sensitivity and context, such items may enhance the learning process. But when those items change hands for inflated sums, driven by macabre curiosity or more sinister motives, serious official scrutiny is necessary.