But what purpose do they actually serve?
Silver_Surfer:
But what purpose do they actually serve?
they flash orange 
had mine from Spain aranda de duero on the way to Madrid ( shell garage 50 clicks north of ) big magnum with MACK stickers on the front! 
RED CAPS waved me through at irun! 
They are a combination light/indicator, so they serve two purposes, they help idiots who don’t have the ability to see a 55’ lorry and tell those same idiots which direction said lorry will be taking HTH
I`ve seen a combo version recently with white light to the front, and red showing to the rear, and what appeared to be the orange indicator in the centre.
Also available in 5/6 LED versions
Ah, so it’s just an extra indicator then, I see.
I kept seeing them on vans in Germany last week. Fitted to the top rear corner. They did look useful to show your indicators but vulnerable sticking out like that.