First of all, by default scroller is not always visible. It is visible when you enter your view but then it disappears. What is more it is not best, from user experience point of view, to display them all the time.
So, to indicate to user that "somewhere at the bottom there is something" you can do this two things:
after your view was loaded in - (void) viewDidLoad
you can blink with scrolls by using:
[scrollView flashScrollIndicators];
and also you can place your buttons, near the bottom edge, in such a way that half of button will be visible and half will not. That will be indicator to user "hey! there is something there!" (http://imgur.com/P9qzUVC)