CZJ Biotar - help identify unusual red marking

[Herb]

This is a preset Biotar 58mm f2 with Exakta mount. The lens has a blue coating. The aperture diaphragm has 12 blades. Can anyone identify the red mark that looks like a cross with three bars? What does it indicate about the lens or coating?

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Many thanks!
Herb

[Brian]

I would expect the "T" to be there. If you get a close look, any chance the "T" was damaged and filled in with paint? Is the three-line mark all engraved, or just painted. Sometimes, the beauty rings get scratched when working on the lens.

The "T" stands for "Transparent", ie passes more light, on a Zeiss lens. I have never seen this mark.

[Herb]

I would expect the "T" to be there. If you get a close look, any chance the "T" was damaged and filled in with paint? Is the three-line mark all engraved, or just painted. Sometimes, the beauty rings get scratched when working on the lens.

The "T" stands for "Transparent", ie passes more light, on a Zeiss lens. I have never seen this mark.
Brian,
There is no red T anywhere on the ring. The three bar mark is definitely engraved as well as painted -no signs of scratches or inadvertent marks on the ring. Whatever it is, it was put there intentionally.
I've searched a whole variety of online sites that deal with Zeiss lenses, with lenses for Exakta etc.ect., with no luck. Puzzling! Any suggestions for further searches? Does Zeiss have a history section that I could search? I couldn't find one.
Thanks for your reply!
Herb

[Herb]

Brian,
There is no red T anywhere on the ring. The three bar mark is definitely engraved as well as painted -no signs of scratches or inadvertent marks on the ring. Whatever it is, it was put there intentionally.
I've searched a whole variety of online sites that deal with Zeiss lenses, with lenses for Exakta etc.ect., with no luck. Puzzling! Any suggestions for further searches? Does Zeiss have a history section that I could search? I couldn't find one.
Thanks for your reply!
Herb
Hi Brian,
Finally got some interesting info re the three-bar red mark on the Biotar. It is supposedly a transition between the single-coated early post WWII Zeiss lenses, which were not heat treated and remained vulnerable to scratches and a subsequent generation of double-coated and heat-treated lenses. The latter coatings were harder and eventually were adapted as standards and marked T*, as in the Opton lenses. No documentation for this hypothesis - just the recollection of a Zeiss expert in the States.