Ancient houses have cornices or other structures that fit perfectly well to pigeons. However, pigeons are a nuisance, both for the inhabitants (noise, health issues induced by the droppings) and for the building themselves (corrosion by the droppings). Thus most cities use various mean to limit their development. In Trento, they have installed on the cornices standing wires (enlarge the photo) that are hardly visible (only the photograph’s eye noticed them while he was drinking a beer!). The wires are too soft for the birds to perch on them and to strong for the birds to flatten them. Apparently, that works!
Trento is a relatively safe city. The city is small, and the people are all very friendly. Even the train station is safe compared to train stations in Rome and Naples. Do watch out for teenagers drinking late at night around the Duomo.