I signal all the time. In a busy city centre, on a quiet country road in the middle of the night. I work on the principle that if someone sees my signal then it has done its job. And if no one sees it then who knows and who cares. It is like the old philosophical question, "If a tree falls in a forest and no one is around to hear it, does it make a sound?".
When I did my driver training with Stagecoach I was told to signal whether there was anyone there to see it or not, a policy I had adopted since learning to drive at 17. I would rather the driver in front signalled by rote than did not signal at all. I also
always manually cancel my indicator, once it has served its purpose. Drivers who wait for it to cancel automatically can drive miles with it still flashing.
When leaving a dual carriageway I start to signal at the 300 yard marker and cancel my indicator as soon as my wheels cross the line for the slip road.
In town, I am very particular about not signalling too early. On my test, 50+ years ago, I was told to make a right turn into a particular street. I started to indicate and then realised there was an opening before the one I was to take. I said "Oh sh*t", and cancelled the indicator before signalling correctly for the junction I was to take. When it came to the Highway Code questions the examiner asked me "When should you start to signal for a turning?", to which I replied, "Certainly not before you pass the previous turning, as I did". The examiner said "I guessed you had realised your mistake". I have stuck to that principle throughout my driving life, even my boy racer days! And when I sat my test you had to do a section of the test using hand signals. A couple of left turns, a couple of right turns and a couple of slowing down manoeuvres. Most drivers today wouldn't have a scooby how to give a hand signal, even though they are still in the highway code.