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..
Mark
It’s hard to tell; and different kinds of Chinese writing are used now than may have been commonly used when and where it was made.
I just know it’s not Korean :-)
I thought at first it was inside, but then the OP seemed to indicate that it was outside.