Thanks to Lyric1 for finding me the info for this skin.
This Sherman Firefly named "Zemsta II" (Revenge II) fought with the 3rd Squadron of the 1st Krechowiecki Lancers, one of the four regiments of the Polish 2nd Armoured Brigade. Rather than the normal British Army number and letter ID codes the Brigade's Sherman tanks all had Polish names painted on the hull sides in a large font to identify them. The 1st Krechowiecki Lancers' tank names were painted in yellow and all began with a "Z" while the regimental symbol of a horses' head was painted within the squadron marking.
The Brigade fought in the Italian campaign from May 1944 until the end of the war in Europe as part of the 2nd Polish Corps, first at Monte Cassino and later at Ancona and Bologna.