If there is pee, there will also be poo. Have a gander and see if you see any droppings. They're like little black pellets the shape of zeppelins (if you've ever had a hamster or gerbil, they're similar), if you can't find any I'd be very dubious about mice. In my experience from having them, you hear them scuttling at night. If you're worried, you can get humane traps for pretty cheap - definitely cheaper than an exterminator.
I don't remember seeing any poop. Maybe I'll go up and check again. He also showed me some gaps in the insulation and said that's made by mice to get around. . He also said the insulation is 12 inches which is low and to gave me a quote for $8000 to remove existing insulation and blow new insulation (because there would be rat poop inside). Or $6000 to blow on top of old insulation.
I think they typically use a black light to confirm that, don't they? Rodent urine should glow. If you have one, shine it on that spot and see if it fluoresces.
Fun fact, cats aren't actually very effective at killing all the rodents. They've done studies and basically the cats just make them really skiddish and they hide so you never see them. They kill one here or there but the real benefit is getting them out of sight.
Every attic I have been in that had mice had tunnels through the insulation where the mice were going through. Like actual tunnels, not gaps or disturbed insulation.