I don't know if there will be police and/or civilian helicopters. However as I was playing Arma earlier, I was thinking about how a cop might tell a helicopter to leave an area without shooting at them.
My Idea:
Every helicopter/car has a radio to start with. The cop may use their own personal radio to contact the person in the vehicle like cops do IRL via radio (well for helicopters anyways). That way, there is no need for confusion and such.
This not only adds to immersion but could be good functionality in order to preserve order and reduce the chaos with cops shooting at everyone/everything. No need to shoot down helicopters if you can't even communicate with them.