I accidentally discovered goof off Pro Strength works pretty well. I was using it to remove mold from factory caulk and discovered it works on black streaks also.
Just dampen the corner of a rag and wipe just the area of the mark off. But first try it somewhere nonconsecutive first to see what happens. Also use white rag or rag color will transfer to RV. and I would probably keep it away from decals.
2019 Forest River Forester MBS 2401R