In England we call them "Indicators" as opposed to turn signals. My driving instructor said, they are call that because they are only indicating they might go that way. Never assume they will. It was some defensive driving advice.
I can understand that it's annoying that inconsistent use of turn signals is an annoyance, it isn't as bad a people that don't use them at all, but my understand is that the American road system doesn't have roundabouts like we do, which kind of require good indicator use for smooth driving.
I've driven in England and New Zealand, and they really had them everywhere.
Yes, we have them in the US, but we don't have enough of them that you can expect that all drivers know what to do with them. It's entirely too common for approaching drivers to be unaware that they must yield to vehicles already in the circle.
I can understand that it's annoying that inconsistent use of turn signals is an annoyance, it isn't as bad a people that don't use them at all, but my understand is that the American road system doesn't have roundabouts like we do, which kind of require good indicator use for smooth driving.