Neat find. It’s a ‘yantra’ ring, and Hindu rather than Buddhist. The geometric symbol is a Hindu sacred diagram known as a ‘yantra’, used for meditation and to attract specific spiritual or material benefits, such as wealth, protection, or inner harmony. The seated figure is not likely to be Buddha (although some Hindus do worship him), but I’m not sure which of the many Hindu deities it is. Most usually it’s the goddess Lakshmi (to bring prosperity and clear away negative energy), or Lord Shiva (the Supreme Being and god of destruction, but in a positive sense to enable the universe to be reborn.) There are a number of other possibilities though.