It might be a proverb or charm, especially if it’s on the outside...
I couldn't really discern if it was on the inside or outside, but it does look like it is perhaps is on the outside. It may be what is does say, some kind of expression. Hopefully my friend can tell me more when he gets home, as he is out-of-town in Florida at the moment., so the phone screen is too small for him to really look at it with any detail. But he thinks it is Japanese at this point..