The Red Army had no universal system of tank markings used during the Great Patriotic War, and commanders developed their own systems, sometimes changing them frequently to prevent the enemy from figuring them out. This was not the case before the war, as a standard system of markings was used.
The markings were split into two separate elements: stripes around the turret and numbers inside a square on the hull. The colour of the top solid stripe indicated the number of the battalion in the regiment: red for 1st, white for 2nd, black for 3rd, and blue for 4th, yellow for 5th. The dotted line below it indicated the number of the company. The same colour scheme was used, but without the option for a fifth company.
The square on the hull represented the number of the platoon, with red for 1st, white for 2nd, and black for 3rd (there were only three platoons in a company, blue and yellow were not used). Finally, a black number painted in the square represented the tank's number in the platoon.
Interestingly enough, this marking guide also shows the tanks with disruptive camouflage applied, an uncommon feature of Soviet tanks.