The whole point of signals is because you don’t know when you haven’t noticed that someone is around. People who only use signals when someone can see them are doing it wrong as much as those who never use it. Cars have blind angles and you can’t be aware of everything going on around you all the time. That’s why you signal, so everyone has clear indication of your intents. You also reminded me of an uncle who used who always forgot to signal before a maneuver and when he realized mid-turn he would then use the signal. Like, it is of no use anymore.