Probably just a grinding artifact, if anything.
The photo you are using has been blown up and brightened up considerably. The original photo, of which your shot is just a piece, can be found here. Blowing up the same feature is inconclusive (it can be found about a quarter of the way in from the right, and about a fifth up from the bottom. It ain't easy to locate.)
The area you are looking at has been ground, so any kind of odd artifact is possible after the grinding process.