The most visibly darkness-aspected of his spells are the portals he uses when he doesn't want to have to walk super far! They look roughly like this, and if any NPCs would be able to tell, he's been staying with three settlements of Solvunn! (Mostly the primary one, since that's where he knows the most people right now.)

With the exception of his combat spells (which he has not been using at the moment), any other of his spells - to fix up the house he's taken up residence in, for example - would not be visibly darkness-aspected.