we need to see images of the marks, to understand more about the maker of the ring. There is also the possibility that the mark is not registered. Images needed for research are One close up photo, another photo of the mark and surrounding area, and a third photo of the entire ring.
The restless blue to violet color of Tanzanite is due to the gemstone's optical properties, that vary, as the crystals respond to different directions of light. The color of Tanzanite, can take away the breath.
David, what we can say considering the age of the ring, unrelated to the mark, which we cannot see, relates to the gemstone, Tanzanite which was only discovered in 1967, in the Mererani Hills of Northern Tanzania near Mount Kilimanjaro. Officially the gem, was called "blue zoisite" and marketed as Tanzanite by Tiffany & Co.,
If you would like us to research further, you will need to send in three images as mentioned.