I have a Native American Indian ring with coral and turquoise on it, and the hallmark on the back reads: MARY (then there is a capital A that comes down beneath the names and there is a line going from the middle of the crossbar of the "A" downward, making the A also look like an arrow, then the name MATT. The names Mary and Matt are all in capitals in 1/16 Gothic print. Does anyone know who owns this hallmark?

This is what I have found about your piece. The 'A' hallmark is an 'A' and a 'T' combined to form what looks like an arrow, it is the Hallmark for Atkinson Trading Company in Arizona, and the names Mary and Matt are probably two people that worked together for that company and made that piece. But without seeing the piece and the hallmarks myself I can't say all that for sure, but I hope it helps.
Heather Ramon