At first blush, it makes sense. If you don't know from whom you are stealing an object and don't really care who the owner is as long as he or she is a Jew, just give it that nomenclature of being unknown. UNB has a certain edge to it, a Nazi edge, the edge of a Nazi thief plunderer who remains completely indifferent to the plight of his/her victim, in this case his/her Jewish victim. SS Colonel von Behr is the nominal head of the ERR in Paris. An unpleasant fellow, former director of the German Red Cross--try that on for size, German Red Cross and SS uniforms all folded into one cozy suprematist image. Mr. von Behr is very aggressive about his anti-Jewish mission in occupied France and quickly teams up with a local band of thugs, former police officers and inspectors as well as hardened crooks and criminals, the infamous Paris Gestapo or the Bonny-Lafont gang, or what will become sadly known as the 'bathtub gang' because of its members' proclivities towards torturing to death their mostly Jewish victims in bathtubs filled with ice cold water inside plush apartments nestled in the better neighborhoods of Paris.
From late 1940 to the end of 1941, von Behr is hard at work ordering the ransacking of Jewish-owned apartments and shaking down wealthy Jews across Paris. The fruit of his thirst for material goods that don't belong to him ends up fitting into close to 60 crates sitting in the Louvre. They are all marked UNB or unbekannt or unknown owners. And so begins the story of the UNB objects.
From von Behr's roguish and uncontrolled antics as an anti-Jewish plunderer, the ERR settles in and rationalizes its illegal acquisitions of Jewish cultural assets. Many paintings and works on paper that are seized fit into the broad category of 'modern'---in Nazi-speak, that becomes 'degenerate'. Those hundreds of 'modern' items are placed in separate rooms awaiting an uncertain fate. Quickly, ERR staffers forget how these items even entered the Jeu de Paume and when they return to them more than a year after their confiscation, the institutional memory of how and from whom is lost, hence they become UNB. But, because many of these works belonged to high-flying collectors and dealers in and around Paris, they bear labels and other identifying markings on their backs. So, from UNB, they can actually be assigned to a particular owner. But, bureaucracy being what it is, the ERR staff will end up inventorying these items as UNB, noting however that they could be matched up with specific owners like Paul Rosenberg, Levy-Hermanos, Weil-Picard, etc...
My particular concern today was the numbering sequence. If you follow the numbers, there should be 4059 items labeled and inventoried as UNB. And yet, there are not more than 440 for which a description has survived. What about the other 3500 or so? We continue to investigate what they were and where they went.
Last but not least, most of the UNB items were seized before or during the Mobel-Aktion (M-Aktion) which began in spring of 1942 and ended two years later, leaving behind desolation and empty, wrecked dwellings across occupied France.
Therefore, UNB owes its existence to the violence of the ERR's methods in occupied France against those whose identities did not matter when they entered their dwellings to steal their property.