This stamp Scott 9N589) was issued in 1990 to commemorate the 200th anniversary of the invention of the drehorgel in Germany. The drehorgel is essentially a German version of a barrel organ or fairground organ. it uses a hand crank to generate wind which in turn blows the pipes. Many of these instruments were placed on wheels for ease of portability; the one shown in the stamp is hung by a strap around the neck. The stamp was issued May 3 for Berlin; as such it is one of the last stamps issued before the Wall fell and Germany was re-united. Here is a helpful article to understand this instrument.