When I was a lot younger and doing my car test the instructor moved the interior mirror a fraction out of line so that I had to turn my head to see behind me, it worked, so if you can remember to just turn your mirrors out a bit so you have to move your head to see in them the guy behind testing you will know your looking, whereas normally you just flick your eyes over the mirrors to spot the dumbarse coming up behind, you get the benefit of not only knowing what's behind you but can be seen doing it. Just a thought as I did my test in 1968 and things have got a tad more complicated, I don't expect I would pass now and would be told to hang up my leathers and stay indoors