Thanks everyone for their comments and for taking the time to chip in.
I find, after 30 odd years on a bike in London and country, that drivers do see me OK day and night and, like most riders, I do generally ride assertively on busy roads. However, on many roads, a cyclist riding in primary will not stop all close passes even if they are forcing cars to cross the centre line to overtake.
I don't want to be an a**e to other road users as I've seen the negative impact that can have (so that rules out for me POLITE jackets, assertions about reading the Highway code or pictures of cameras); I just think that reminding motorists to give cyclists space somehow will reduce some of the unpleasant experiences I have had recently and could be a way of reducing the fear that many cyclists have about riding near traffic on roads.
And I'd like to do it in a suitably stylish way without using an industrial-sized windbreak.