One of the features that changed for Assassin’s Creed 2 was that the main protagonist, Ezio, was able to wield two hidden blades. Early concepts depicted this right blade as coming out of his sleeve, whereas in the game there was a vague indication that this blade actually differed from the hidden blade he received from his father, Giovani. The closest you could see this design was on the unlockable Armor of Altair found underneath Monteriggioni.
Looking at the concept art, you can see that Ubisoft indeed had this fully mapped...
