Having done some flying in the good ol' USA where you are encouraged to yell 'Clear Prop!' (I'm softly spoken so no one ever hears), I found myself back home at my local airfield. About to start my engine I observed an instructor and student at another aircraft parked alongside. I earnestly called 'Clear Prop!', no one heard. I signalled engine starting with hand signals several times to a now bemused looking pair. Then the instructor walked over to my aircraft through the prop arc, put his arm over the front cowl and helpfully asked if everything was alright!
Never earnestly assume that everybody else knows about hand signals and prop safety.