Sorry if this is a really simple question- what was the purpose of the white stripes around the turrets of tanks?

I belive they were for air identifaction. I think these came about late 44 or early 45. I know a lot of the ones in the Berlin invasion had them.

a number of JS-2s definitely had them. But I'm not sure whether these were for air recognition simply because aircraft pilots would not be able to see them. Would'nt you need a mark on the top of turret or hull to be visible from the skies?

Correct, the white stripes were for ID...not just Air ID though, as the stripes on the sides were helpfull for ground units as well. However, the germans were quick to adopt them as well since they were not really in danger of being attacked by the Luftwaffe once this system was put into play (1945).

According to a variety of sources, the stripes were added to the turrets of Soviet tanks to help U.S and Commonwealth ground attack aircraft in avoiding "friendly fire" incidents on their Eastern Allies's tanks.
They seem to have been applied as the Russians were closing in on Berlin.
I don't imagine that IS-2, T-34/85 and various SU crews would appreciate the aerial "attention" from U.S. P-47's, P-51's or RAF Tempests and Typhoons.
Geometric shapes (Triangles, Circles, etc...) were also applied to turret roofs as a means of identification.
The Germans supposedly twigged to their meaning and started to apply them to their few surviving Panzers, though I've never seen any photos confirming this.
If anyone has any info i.e. photos of any German vehicles so adorned, I'd love to see them.
Cheers

jjumbo