The latest installment of Big Ten Basketball: The Journey showed a brief closeup on Beilein writing on a white board in the locker room at the BTT, with the ring prominently visible on his hand. I don't have a screencap but I can confirm that the ring, in fact, has an M on it, so it's not from his time at WVU. It's still uncertain what the ring is for. If it's indeed commemorating something he's done here, the obvious candidate is making the tournament two years ago, but giving out rings to make the field doesn't seem like something we'd do. My guess: we gave him the ring in honor of his 500th victory at a four-year school, which he achieved in 2009 (he has 543 wins now). But further investigation is necessary.
spoiler alert: i linked this