Interesting question,
I was taught to shout 'Clear prop!' while learning in a Cessna 150 at Cranfield. If I was accompanied, the instructor would usually say 'Clear my side'. The key was turned as soon as the little window thing was latched.
Slipslider, I usually put the intercom on after engine start.
The checklist seems to say, 'Lookout with care all round. Through open window shout 'Clear Prop'.
I have since taken the opportunity for a good loud shout, it's not often I get the chance.
However;
I've never had anyone answer 'No it jolly well isn't!!'.
At Cranfield the planes are parked quite close together and I suppose that it is possible that a very new student or a passenger might be walking along the line or even picking up a stray object from beneath the front of my plane, having missed seeing me while I reach down on the floor for a dropped pencil or similar.
Suppose the general public were walking about on an open day or waiting for their friend to come back from a trial flight to take some photos ?
Self 'CLEEEAAARRR PRRRO-O-O-O-PPP!!!'
Person 1: 'What did he say'
Person 2: '"Clear prop" I think'.
Person 1: 'Is that the thing that holds the plane up ? with the wheels on the ends ? perhaps we should get out of the way of them ? quick step back!'
Chugga Chugga OOOoooowwww!!!
It's possible.
How about "STAND CLEAR OF THE PROPELLOR, THIS AIRCRAFT IS ABOUT TO START!!!"
Trucks use something similar for reversing and it seems to do the job, or at least absolves the operator of responsibility.