The 1932 system of tank identification involved two bands of paint around the upper turret. A continuous stripe at the top denoted the battalion, and the dashed line below that indicated the company. S
1st = Red
2nd = White
3rd = Black
4th = Light Blue
5th = Yellow
o a tank with a solid red line and then a dashed red line would be 1st battalion, 1st company.
They could identify the platoon by placing an outlined square on the side of the turret, using the same colors above. So adding a yellow square would mean the 5th platoon.
This system was phased out in 1939, but many tanks still used this in Poland in 1939, and against Finland in 1940. And some tanks still used this system in June 1941.
By 1939 there were new systems in place, but nothing officially wide-spread. Different units would use circles, diamonds or squares.
The reason many unites used a diamond was because it was the standard soviet map symbol used to denote a tank unit.
Some regiments went with the cyrillic alphabet, in the standard order for that alphabet.
1st Battalion companies were A, B and V
2nd Battalion companies were G, D and E
3rd Battalion companies were Zh, Z and EE
4th Battalion companies were K, L and M
The company letter and the vehicle number were painted below the diamond. So the diamond up above with the funky H 2 below is actually an "EE" so that is the 2nd tank of the 9th company, of the 3rd battalion.
In addition to the turret identification markings (to help coordnation between tanks and units), they had symbols painted on the turret roof to help prevent friendly aircraft from attacking. These symbols were often painted in whitewash, so they could be easily scrubbed off and change.
The symbols were changed ever 2-3 days in the middle of the night. Here is a 10 day sequence (mid-July 1941):
White Triangle
White Circle
White Rectangle
White Square
Sometimes they would change it up and instead of one large triangle (for example) they would go with two smaller triangles. The normal single symbols were 2.5 – 3.5 feet across, centered on the turret top.
And sometimes, just numbers (either 2 or 3 digit) were painted on the turret sides. I have lots of books showing mid-war and late-war tanks with 2 and 3 digit numbers on the turret sides, sometimes with a star, sometimes not.