The Cold War was a state of political and military tension after World War II between powers in the Western Bloc (the United States, its NATO allies and others such as Japan) and powers in the Eastern Bloc (the Soviet Union and its allies in the Warsaw Pact). Historians have not fully agreed on the dates, but 1946-1991 is common. It was "cold" because there was no large-scale fighting directly between the two sides, although there were major regional wars in Korea, Vietnam and Afghanistan that the two sides supported. The Cold War split the temporary wartime alliance against Nazi Germany, leaving the USSR and the US as two superpowers with profound economic and political differences: the former being a single-party Marxist-Leninist state and the latter being a capitalist state with free elections. This mod presents the player with many Communist and Capitalist nations in a scenario where war has broken out between the Warsaw Pact and NATO/UN nations.
There is no certain evidence that Polish soldiers dressed this way during the 50's. In fact, there is almost no records that indicate how the Polish uniforms looked in the army during their Soviet Bloc days in the 1950's
Hard to see from the image size, but looks like the emblem on the tank has the crown on the bird's head.
It's just image warping, there is no crown :)