WWI German Occupation of the East, 1916  Lithuania Wilna to Poland Warsaw. 78 reichspfennig Germania stamps overprinted w. Ostland cancelled 17/6/16. 
The back shows verity of  canceled  29/6/16 Warsaw Poczta Town post stamps. All cancelled with bridge double circle bridge ' K.O.m.st.W / Poczta Miejska / b':

• I Syrena (coat of arms of Warsaw)  Fischer I | Michel I | first issue of Warsaw's town post stamps; 
• Bisect of Fischer 1 Syrena Syrena ; 
• Fischer 7 | Michel 8 | Issued 22 November 1915 Fischer 1 surcharged with a black "6 6" overprint. The number 6 is wide. ; 
• Fischer 10 | Michel 10 | Issued 2 February 1915 "6 gr." overprints with two rosettes.