Gee Fred,
I am glad you are not a Dr. because with your record you would have massive malpractice suits against you for your "guessed" diagnostic abilities.
Before you ask, it looks to be acid etched. As far as I can see it is just discoloration or "if in fact" it is a defect in the etch, most likely a defect in the template.
Since you can never be wrong I am sure you will have a response but, my record is far better then your school of witchcraft.
Happy New Year!
Bob