If it's caulk you'll be able to rub it off using a very mild solvent product. If it's a scratch, then the issue becomes more complex...Is the panel on which this blemish resides made of fiberglass?...then, you don't have paint
that is damaged; it's gelcoat
...the same stuff used by the marine industry to cosmetically surface the vast majority of boats. Repair to gelcoat is not difficult, but a bit time consuming. Rather than get into the details, determine whether the blemish is indeed a scratch...if it is, there are many, many sources on the internet which will guide you through a successful repair. Check out boating sites. As a long time cruising sailor, we all have gone through this and made repairs to our gelcoat/fiberglass. Good luck.