"Berlin, W. 35 *d 6 7 89" - single circle postmark, KBHW 575, not zustellbarer, retournierter local letter, appropriate note front- and reverse, to determine the sender was the cover postal service official opened, reverse blue paper seal "imperial German city post office Berlin". A nice and interesting document, you would note also the Stamp date with the Zahlenreihenfolge 6-7-89