That's my favorite trick , although I haven't as yet noticed any police actually watching me I do it as a precautionary measure. I suppose mirrors are essential for high speed ebike riding.What prompted my thread entry was that a local officer who'd seen me riding electric bikes for years and normally taken no notice, was obviously following me at just over 20 mph, albeit with me pedalling. Luckily I use a bar end mirror in my urban area and spotted him, so I simulated both huge pedalling effort and gradually lost speed, faking out of breath as he then passed.
In over 20 years of cycling I've only once been stopped by the police and that was for not having lights. I was 16 at the time and they were pretty nice about, infact, given how silly it was maybe too nice.
I'm guessing that electric bikes really aren't on the police radar at all. Infact I really wonder how many people know my bike is electric and how many just think I'm a superfit cyclist. Do they(police) even have the kit to check for speed in car? And even if they did they'd have to prove that it was the motor and not pedalling. I can't see how they'd do that without siezeing the bike and taking it in for an analysis.
I think all this might become an issue if electric bikes become really popular and invevitably, we will have people riding badly at 22mph and causing accidents/scaring people etc.
That said, if ebikes actually become popular we might just have the political clout to bring in more just laws.