Mark /smudge on sapphire screen that won't come off

Hi,

I noticed this about a week after getting my garmin. It's only observable at certain angles so I have a feeling it was always there. It kind of bugs me as I think it will affect the resale value when I want to upgrade..

Anyone have an idea of what it might be? It really doesn't look like a physical imperfection like a scratch. It looks like a smudge or a defect with a coating on the screen (I'm not sure if there is a coating?). The photo below is the best I could do to capture. Sorry about the dust, it was hard enough capturing the right angle for the smudge to appear.