Hint, Failure, and Success captions are all related to specific interactive objects such as click boxes, buttons, text entry boxes, etc. The Hint caption usually appears on mouseover of the interactive object (as Lieve mentioned). It's intended to help the user find that interactive object and know what to do with it. These hint captions are not designed for the slide as a whole.
It sounds a bit like you just want some captions to appear that will give the user info about what to do with the slide. For that requirement, you can just add some ordinary text captions and format them to look like your Hint captions.
