The Hint button is a key/button (B on Xbox 360, Circle on PlayStation 3, customizable on PC) that, when pressed, turns Faith's view in the direction she should be going.

For example, on "The Edge", when Faith Connors is outside, the player can press the Hint button, turning Faith towards the red tower she has to get to to meet up with Celeste Wilson. This helps the player by showing them the general direction they should go. The button also helps by pointing at wall edges, doors, and vents the player needs to interact with.