Meaning of plexiglass symbol?

Good afternoon,
Was working on a Cosmic 166026 today and noticed when I removed the old plexiglass a symbol that I have never come across earlier. First I thought it was a well placed scratch, until I put it under the microscope. I cant find any information about this particular version, anyone know the history/meaning?
The plexiglas has a grove for the tool 107, can it have anything to do with this? I have probably worked with over a hundred cosmics, and never seen this...
Lets see if the forum can deliver this time😉

Cheers

It’s to perfect to be a “missprint” and I can’t imagine that a fake would have this additional arc, so I assume Omega has had some purpose with this marking. Hopefully someone else has seen this, if so it would be interesting to know on which reference.