how do you inlay a coin in the riser of a bow?

Buy a forstner bit the same size as the coin, drill only to the depth of the coin and then epoxy in.
Burnsie

Yup!!

Yep, a forstner bit is the way to go. I've done a compass inlay on a couple of bows. I had to special order the bit because of the diameter of the compass but you can get the size you need. Don't settle for something close.