Oh they have sirens, klaxons, bells and warning lights that go off when they reach 70. There is also a spring loaded boxing glove that thumps the driver.
However as European law requires speed limiters set at 56 mph you never see them.
(Incidentally there is no law requiring reversing horns, and many do not have them.)
you should stop the driver next time and ask politely if in future they can drive at 70mph and then do a handbrake turn, thus avoiding a reversing manoever. Thats got to be safer than having to go backwards with limited vision. :)
i hate the one which has some bint shouting 'warning this vehicle is reversing' the dray that delivers to the pub next door has this one and they wake me up most saturdays