I've been doing that for the past 22+ years and I wouldn't care a fig if someone thought me funny for doing it. I do it loudly enough to get a startled look from someone in the middle distance - achieves its purpose - great!
Yes, I'd say that there's a slight lacking of airmanship in someone who doesn't do everything they can to ensure no-one's going to get hurt when they start the engine.
As to the US not understanding it; I bought a tee shirt last time I was at Kermit Week's Fantasy of Flight. It depicts a mechanic astride a Wright Cyclone with an aghast expression on his face as the words 'clear prop!' explode in a bubble adjacent. I'd say that it's well understood in proper aviation places.
Of course at work, no-one would be heard - can you imagine Nigel winding open the DV window on a 777 to announce his intentions? - so we rely on anti-coll beacons being switched on.
Cheers,
The Odd One