1873 (Jun. 12) Cannstadt, Würtemberg to San Francisco, Cal., blue registered mail return receipt with two-languages (German and English) sent with a registered package to San Francisco, recipient signed receipt and sent it back to Cannstadt, Württemberg in the mail, no postage was required, Very Fine. Estimate  $150 - 200. The U.S.-North German Union postal convention of 1867 provided for registered return receipts. No other postal conventions before 1875 required this feature. Example of these returned receipts are seldom seen. Of the few seen, most were returned "out of the mails.". $0 (Image)