USSR. 1928. Registered letter sent from Moscow on April 6, 1928.

Cover of registered letter sent from Moscow to Vienna (Austria) on April 6, 1928. Letter passed foreign exchange control, tax paid by stamp 5 k. with variety in overprint: missed "И" in word "ФИЛАТЕЛИЯ" / "PHILATELY". Letter passed foreign exchange control during the transition of authority from Commissioner for Philately and bonds to the All-Russian society of philatelists. Very rare cover, known up to ten items of this period.