Get Some F**king Lights

Is there widely accepted hand signal/gesture for other road users to warn them to turn their lights on? The I saw 4 cars on my way home today without either lights on...I must have been doing something wrong because none of them knew what I way trying to convey with my random waving of hands.
I try "flashing" them by covering and uncovering my light, but it's not very effective. Sometimes works if you're trying to tell someone to turn off full beams though.