Whats Wrong with my breitling

[Kersh2312]

Hi noticed this on my watch which I bought used from a large watch dealer
The surface feels smooth with no visible marks on the outside yet when I hold it in the light in a certain way it shows a mark
Not a scratch but a blury crescent shape
Just tried uploading a photo don't know how to do it
Anybody got any ideas what it could be
Cheers

[Gazzab]

Under the glass? Maybe damage from condensation/water?