A red sign usually indicates danger, hazards or the unexpected. In this case, this sign is telling people not to smoke in them surroundings as they may put themselves in danger. For example, this could cause a fire if they dropped their cigarette.
The yellow sign cautions people that the floor is wet and that this is a potential hazard to the people in them surroundings. This helps them to be aware and prevent themselves from falling over and injuring themselves.
The green sign shows people what way they would go to get outside the builiding in the case of a fire. This prevents them from getting stuck inside the building in the case of a fire or fire drill. This could save lives.
