This is a German prestamp cover from Parchim, Mecklenburg-Schwerin.
The Feuser/Muenzberg Deutsche Vorphilatelie Stationskatalog lists it as #2690-6. Chronologically, it is the 6th type of marking for Parchim. First recorded use is 1830, and a value of 20 DM ( approx. US$10) is given.