I usually wave (more like a salute) with a forward motion, but then, immediately, turn my eyes back to the road, so I usually don't know whether someone returned the salute, and it is not so important. I do it to make the other rider (or runner) feel acknowledged and supported, not so much to gather or elicit the same.
So, again, I do not take my eyes off the road in front of me long enough to wait for a return salutation. If they do, then great: I hope they think I see it.
As far as manual gesticulations go, I fully understand that many riders do not wish to take their hands off the bars, so if I get no reply, that's fine: I'm glad they are vigilant and opt for the safer measure.