You will see a person pointing a firearm at you and you will see the diode emitting a color. That's in daylight. In a darker environment you will likely notice a dot on you. It is true that do use smoke and fog to exaggerate the beam on TV and movies. Basically if you are close enough you are going to see the guns laser diode in all but very bright conditions. If in doubt sweep that laser across their face, they'll see it. You wouldn't be pointing a firearm at them if they weren't a perceived threat so I doubt if they ran off they would run to the police or a lawyer. Even if they did you avoided having to shoot them, threat neutralized without firing a shot.
I've posted about several incidents where this has been exactly the case, over the past few years. One particularly memorable one, where the perpetrator was actually in the process of robbing some anti-firearm ingrates I had crossed paths with mere minutes before, actually defecated on himself out of fear when he saw the laser dot from my EDC on his body, and then ran off leaving an unpleasant reminder in his wake. It is a fine teaching moment.