Nigel replied:

Very good advice. I remember when trucks used to use their indicators to show when it was safe to pass, but it doesn't seem to happen anymore. I get the impression that most truck drivers have put up with one too many bad car drivers, and they don't want to help out anymore, but taking the time to talk to them on UHF and thanking them when they are courteous helps to break down the barrier between trucks and other road users.

Frank replied:

Its very dangerous, a truck might put his right hand indicator to turn & you might think he is signallingn you to pass.