As a property insurance adjuster for over 10 years, I've seen how excessive candle burning or improper fireplace operation can produce soot that is attracted either by static charge or gravity (anything with mass has a gravitational pull on a tiny mass like a soot particle) to surfaces of opposite charge or greater density such as the drywall at a stud or truss chord (vaulted ceiling). It will also spot at the nail or screw heads. It could also be dirt from dust that stuck to a damp surface caused by condensation on a cold "stripe" if the attic insulation doesn't cover the truss chord adequately and the wood conducts heat away from the interior faster than the insulated drywall. Try washing the surface with a mild bleach solution. If it cleans up, you have a air quality/surface condensation problem rather than mold or excessive snow moisture. Otherwise, you need to look for roof damage, adequate attic ventilation, and ridge vent design. I've seen where snow will blow in through ridge vents. Moisture from melting snow in the attic space would be trapped along truss chords and possibly soak through the ceiling along them. Good luck.