Thanks for flagging me down as you overtook me on the M25 today. I couldn’t hear what you said, except for “warble-garble-airbags-garble” after that, I was too busy ■■■■■■■■ myself after you’d tilted your hand to mime something wrong with my trailer.
I gingerly stopped on the hard shoulder to check out what, I presumed, were flames and wreckage coming from the back of my lorry… and found absolutely nothing at all. Then it dawned on me what he was on about - because I drive a low profile unit, standard trailers (especially the horrible Tiger trailers that ride high anyway, such as I had the misfortune to be pulling this morning) look as though they’re jacked right up on the air. Unfortunately, I’d stopped on the steepest part of that particular hill, and it took a looong time of kicking up debris on the hard shoulder for me to reach any kind of reasonable re-joining speed! 
Still, kind of nice to know that he thought he’d spotted something wrong and let me know about it.