Jeep, Taco, Mustang, Prius owners all know the wave, Ok, maybe prius drivers don't.
The wave can be awkward though sometimes, because you forget you are at work and not driving said cool car, but rather the cool car with blue lights...
So if a cop waves at you it may just be because the shift work causes them to have no concept of time and they just think your Tacoma is pretty awesome and they would rather be driving theirs through a mud puddle.
Just wave back, don't make it weird... and use all of your fingers (not just the middle one.)