Without knowing a little more about the provenance of the sheet music in question, this answer is a bit tentative, but the stamped marking's language points to this dating from the postwar military occupation of Germany. All four of the military governments had their own licensing protocols for printing materials in their respective zones that would prevent any resurgence of National Socialist ideology or other moves contrary for the occupation government. While these regulations were largely concerned with periodical materials, pre-occupation publishing houses that specialized in politically-neutral topics like the sciences or arts were licensed to restart printing. This licensing process was greatly streamlined if the publisher's specialization meshed well with the larger political imperatives of the occupation government. Such was the case with Breitkopf & Hartel, one of the larger and most prestigious firms for the printing of music and located in Leipzig in the Soviet zone. Not only did the military governments wish to eliminate Nazi and martial music, they put great weight behind the importance of the German musical tradition as a means to uplift and reform Germany.
The cultural importance of German music became enmeshed in the wider emerging Cold War as both Soviet and Western occupation governments sought to claim Germany's musical heritage for their own ends. The Soviet zone's Kulturbund not only sponsored Beethoven revivals, but also concerts featuring Soviet and Russian composers. OMGUS licensed various publications touting American developments in the American scene and sponsored tours of American musicians like Leonard Bernstein, who went on a German tour in 1948. This cultural Cold War led to various banning and restrictions placed against publications produced in the opposing blocs' zones. The quadripartite regime of censorship and licensing had already created the bureaucratic mechanisms to regulate information, but regulations became freighted with new importance in light of the Cold War. Between April-May 1948, the Soviets banned all US-licensed newspapers and OMGUS responded with a ban of Soviet zone publications. Although censorship restrictions eased up in the Western zones, there still was concern that such materials produced in the Eastern zone contained ideological materials, hence the need for a stamp.