How noticeable is it in pics? It will become more so as you stop down the aperture.
It could also cause light to reflect into the lens. If not noticeable, use it as is as far
as possible. Sometimes, a well-placed small black dab of [something] over the mark
can help.

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Oh, forget polishing it, as you'll likely change the figure of the lens, and at
least remove the coating nearby.