Was riding as passenger in a car on 95 South, chatting with the driver, when all of a sudden hear a siren, and then it fades away. Turn to the driver who asks, ‘What was that and where was that?’ ‘Behind us and right,’ I reply. Some miles later, hear it again, and this time, we both comment it must be coming from the overpass under which we have driven, as this sound has corresponded with driving under an overpass both times. Apparently at the same time, both of us look out the passenger side window, and see, two lanes over a car traveling at our speed with a driver flexing and unflexing his hand. And mouthing words. We both look. We both continue looking. Said driver continues in his lane, no car between us, mouthing something and flexing his hand, closed and open. As we continue to watch, he takes the approaching exit. We simultaneously realize he is an undercover cop – hatless – but appears to be wearing a green uniform- in an unmarked car. We, to this moment, have no idea what he was trying to convey.