How do you handle people that visit state or national parks and don't follow the rules?

ie, not paying attention to the signs or just being general idiots
>going off trail and falling into boiling hot water and dying in yellow stone
>taking photos up close of fauna and getting attacked
>walking out onto cliffs and either falling or accelerating erosion


Should I be yelling at or confront the people or silently let them get away with it and notify the park Rangers?