Quite apart from common decency and courtesy, not indicating whilst driving [along with tailgating] is a major cause of traffic congestion which in turn [excuse pun] makes a cyclist more vulnerable.
I always indicate including when cycling unless the road is empty and often get a wave of thanks when I indicate to turn left from the driver waiting to pull out from the same turn.
I am a bit surprised that anyone riding a bike should feel out of control whilst signalling, it's not only driving standards that are deteriorating...this from someone who just recently was hit head on at a combined speed of over 100 mph and the t**t didn't have the decency to indicate that he was going to do so