Here's an interesting one I recently received.
This postcard was sent on 21 March 1917 from Ahrensböck, Germany, to Emma Lohse, a 69-year-old widow living with her son's family in the tiny town of Charlotte, Iowa, population ~400. Frau Lohse had emigrated to the U.S. from her native Germany.
But this postcard never made it. On 6 April 1917, America entered World War I and mail service from Germany was suspended. This postcard was stamped with a box cachet stating "Zurück / Keine Verbindung" (Return / No Connection).

