It's dirt ground into small cracks. Some very gentle and careful work with a magic eraser and alcohol will do it. Just go slow, and less is more.

Some wet sanding with 2k grit and alcohol might do it as well.

Use some Flitz polish from the tube. Not the can. It cuts a bit more than Novus 3 and should remove the line with a bit of elbow grease. Apply on a soft cloth and rub it well. Then wipe off excess.

Note Flitz in the can is a bit more watered down. The tube version rubs out lines like this a big better.

This is the easiest and cheapest safe method.

Thanks
Dougram69

Acetone or naphtha?

Brake cleaner on a rag or RapidTac Remover Cleaner.

Brake cleaner would work only because it's clear coated.

RapidTac