As above. Peace of mind that what you are riding is solid. Rub it down, I'd go to the welds and see if the chain stays are ok. If it's surface, treat it with kurust or similar as this kills the rust, then prime and paint. Worth doing this well as it's in an area that will get all sorts thrown at it.
I had a clockwork that had a repair in that area and the paint had come off. Little rust thankfully but I still repainted the full stays as a precaution and to aid blending of the paint. I used the weld lines to help with the blending where new paint met old.