The month of the Polish-Soviet "friendship".
7-XI-1917 = 7 November 1917. On 7 November 1917, Lenin led his leftist revolutionaries in a nearly bloodless revolt against the ineffective Provisional Government (Russia was still using the Julian Calendar at the time, so period references show a 25 October date).
7-XI-1952 = 7 November 1952, the date of issue of these stamps.
Fischer XXII (Without the Lenin inscription)
Fischer 643-644 FDC
Miesiąc pogłębienia przyjazni polskp radzieckiej
(Month of the Polish-Soviet friendship)