A very interesting set of notes issued in January 1921 urging citizens to vote to remain part of Germany in the March 1921 referendum. The Oppersdorf family, Schlesien nobility, lobbied the citizens to vote to join Poland. This was not well received, and as we see here, the spider bears the name "Oppersdorf." Ultimately over 95% of the inhabitants of Oberglogau voted to remain part of Germany, however, the city is now part of Poland (since the end of WWII), and today bears both the German name for the city as well as Glogowek in Polish, as the city is officially bilingual.
Robert Ball Nachf. in Berlin (the Nachf. stands for Nachfolger which means 'successor(s)') is one of the big numismatic mail-order and auction houses of the 1920s, and they are one of just a few Notgeld dealers from the Notgeld era who actually printed their own envelopes with information about the set contained inside. Some are handwritten, others are typed or mimeographed, and some are even specially printed for the particular note or set that's inside. The envelopes have become quite rare, especially in excellent condition, much rarer than many of the original envelopes that accompanied the sets - to the point that trying to find any particular Robert Ball envelope is usually a lost cause. The company assigned their own catalog numbers to the notes, printed in the upper right-hand corner of each envelope.