Not giving the coppers a heads up is a big bonus. They can hear most bikes coming, especially if the rider is trying to make progress. By the time I pass and they look up, I've gone.
I can certainly vouch for this. I don't yet own one, but I've always kept the quiet, stock mufflers on all my ICE bikes. I used to get frustrated with the
Loud Pipes Save Lives crowd, because I imagined they were creating a bad image of all motorcyclists, but I've since changed my mind.
I now have stealth bikes that didn't cost me a penny. All of the other gazelles on the Serengeti Plain have voluntarily donned belled collars to let the lion (LEO) know that dinner is on the way. I have slid past speed traps with the policeman's radar gun pointing straight at me while going 15 mph over the posted speed limit, and the police don't even bother coming after me. One of them even waved(!) and I was on my wicked-evil ZX9R.
Of course we are breaking the law and this won't work every time, but the police have largely been conditioned to equate speed with noise. If they can't hear us, they generally don't bother.
So I always wave to the nice loud Harley men and stuntaz from my quiet "Newbie" bikes and chuckle to myself when they don't wave back.