Careful here. Even though blurry, this ring looks suspiciously like sterling silver to me.
It is very possible that the p.t is a manufacturer's mark; very misleading if that is the case. An electronic tester could be helpful.
Of course, you need to be careful and have baking soda present, but one drop of nitric acid on the inside of the ring will also quickly tell you. If the drop turns immediately a smoky grayish, brownish color, you have silver. But if the silver is rhodium plated, or if the ring is platinum, it will sit on the ring like a drop of water.
Platinum also has a much heavier specific gravity and will feel heavier in your hand. Another quick way to tell is to buff off any surface scratches. Silver polishes easily and platinum takes forever to polish bright.
Best of luck, and let us know!
