Yeah it took me a few tries to figure it out but basically it is in the new area only and they are little poles with red flags on them.. all you do is basically free run on them and you automatically spring off of them.. it takes a few tries and some patience but its not so hard after you figure it out --- GT: StoriedFob
Partial **spoiler** below... Hold the RT and A simultaneously to sprint...and make sure you are running straight at the spring jump pole thingy. If you veer to the left or right you won't trigger the vaulting motion. Takes a couple of tries.
First time I've seen this used is in the "Artist" assassination scenario (one of the nine Savonarola lieutenants). If you move to the left of the rooftop you are instructed about how to "spring jump" from the jump pole thingy. Problem is that you just make it with one hand and can be viewed by guards while you're dangling. Note that it's much easier taking this guy out by moving to the right and taking a Leap of Faith into the hay wagon below, then jumping out when the Artist strolls near this location.