Its the older style Burt Co Adhesive starting to seep up through the inlay onto the 'lens'
This is another area we researched when looking at possible altered chips.
Allan Myers, Gene or Jim Blanchard can all confirm the above.
The glue mark often takes on a circular shape as that is the shape of the tiny reservoir routered into the blank to hold the adhesive. Approx 8mm across.
If I have time later I will post some pics of chips with inlays removed to demonstrate.
I thought your 'suspect' DI $25 might have been the same, thats why I asked for a scan of the back of the inlay