Hello. A few years ago, my wife got two stoneware mugs at the 4th Street Festival of the Arts in Bloomington, IN. They are our absolute favorite mugs, especially since they hold two cups' worth of tea! Sadly, one of them chipped and then totally cracked and we have been trying to replace it, but we don't know the potter or how to get in touch with them. I have a photo of both the mug and the mark.
The mark looks like it says KyB to me. Maybe it is a Kentucky potter?