"Continuing to signal after the turn is initiated is as futile as using a turn signal in a dedicated turn lane. I mean at that point what the hell else you gonna be doing?"
I have to disagree with both of your comments.
The signals should be operating until after the turn is completed. That's how car and truck self cancelling is designed to work. When the steering wheel turns back the opposite direction, as the car straightens out, the signal is cancelled. So, that means anyone that uses arm signals only, must hold his arm out through the complete 90 degree turn. Of course, no one does that, which makes using arm signals only a poor choice , when flashing lights are so simple to use. Just sticking out your arm as you approach and enter a turn,then dropping the arm as you drive through the intersection, would be considered illegal, but likely not enforced.
The law requires turn signals to be used, whenever a vehicle makes a turn, even if its a dedicated turn lane.