Assassin's creed 2 Where is Leonardo da Vinci's studio? Where is the secret letter? It's better to have a picture

In central Florence (before Chapter 6), in Venice, when a secret letter is found, an L sign will appear on the map (before Chapter 12). After chapter 12, there will be an L sign in the workshop of the manor. Of course, Venice and Foley should also look for them. After all, it will be displayed when you buy a treasure map in the store.