You acquire this after collecting all 100 feathers. You will become fully notorious once it is equipped, so first go to Monteriggioni (the cape is ineffective here). What is important to know is that you DO NOT have to physically be inside each city for this to count, just travelling to the area is enough. Set off for Florence using a horse, then once you appear outside the city walls , head to the Mountains. Come immediately back to Florence, then head to Tuscany. Ride to the travel area outside the city's gate and book a trip to the docks in Romany, then finish off near the Thieves Guild in Venice. Unequip the cape by equipping a different one. Folowing this way will (probably) avoid all conflict and the hassle of a fight.