If you refer to the insignia seen on this Armata tank for example (picture 1 in the attachment), it's the stylized red star superimposed on the "Georgiyevski" ribbon (The Ribbon of Saint George), which is the symbol of victory. The same insignia was applied to all vehicles participating in the parade. On Victory Day the ribbon is also widely worn by soldiers and civilians alike.
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St George is the patron saint of Moscow, when you walk into the Kremlin there is a relief carving above the entrance.