You need to understand that heli's flying overhead are different to cars or motorbikes screaming past as they are rarer and impossible to communicate with (for example you could give the finger to an idiot on a bike, but a bit pointless at a heli as I have learned).
And since when has this made any difference to their behaviour? My guess is that after such a response the next time they'd give it even more throttle, not less.
It's pointless to make a gesture at the pilot, even if they can see you, as they probably are not in a position to avoid your location. They are either taking the shortest (and thus quickest/cheapest route, burning min fuel, causing least noise overall) or they are taking the route they have been told to take by a controller, which is not negotiable.
As far as I can see the only helicopters that you can reasonably take issue with are those on a random sight-seeing trip, who may (if regulations allow) be able to do their random sight-seeing somewhere else. I doubt there are any of these, of course.
The rest you are stuck with, I'm afraid.