I looked up this chip in TCR 15. There are references to an incused and not incused (imitation) check.
I looked at the definition but could not find the photo reference on page 311 of TCR 15.

I suspect that this is a mule but would appreciate opinions. BTW, the discoloration in the photo is not on the inlay.
Also, it is for sale.

Thank you,

Joe Watanabe