This is a postal stationery cutout, as has previously been mentioned.
Specifically, this is a "Rohrpost" envelope fragment. Michel catalogs the envelope as RU 1.
From the 1870's through WW2, Berlin had an extensive tube mail/Rohrpost system running through the city. You could mail a small, specifically-designed envelope, (such as from what your indium was cut), or a small postal card from one part of city to a receiving station somewhere else in the city. Letter or card was placed in a capsule, such as you use at the bank drive up station, and eventually. and efficiently, would reach its destination.
Unfortunately, specialist Germany collectors do not collect postal stationery cut outs, or "cut squares" as some U.S. collectors do with U.S. postal stationery. The reason is because postal stationery of the Germany area can take various formats (sizes, printing, flap shapes, or watermarks) which can only be identified by having the whole card or envelope.
Disclaimer: While a tremendous amount of effort goes into ensuring the accuracy of the information contained in this site, Stamp Community assumes no liability for errors. Copyright 2005 - 2026 Stamp Community Family - All rights reserved worldwide. Use of any images or content on this website without prior written permission of Stamp Community or the original lender is strictly prohibited. Privacy Policy / Terms of UseAdvertise Here