I had a need to display a 'waved' change of surface
flag at Donington today. Considering the wind at the time it was a 'move from side to side' flag instead because there was a constant strong wind directly onto the flag, if I'd waved it all the drivers would have seen was the stick!
That said the oil dropped by a Mini was all the way round the circuit so if the drivers hadn't realised they were either blind or extremely skilful...