How do i get on top of the skate 2 hollywood sign?

I look at all these videos of people jumping off of the hollywood like sign in the game, and getting huge air off of a small incline. How do i get on sop of the cougar mountain sign?|||its a mission you do with the danny way bonus crap and then when you beat all his missions he will give you spawn points in your locations map and one of them will say on top of e and that will be it have fun!!