Sir, – I recall overseas visitors being solemnly advised that L (ie, learner) and R (ie, restricted to 45mph in the year post obtaining your full licence) plates on Northern car windows stood for “Loyalist” and “Republican” so that people would be able to recognise/avoid each other in car parks etc. Given the tensions of the times, this tall tale was, on occasion, believed.
Generally, perhaps we could have an NB (“no bulbs/nota bene”) sticker made of reflective material for those optimistic souls seemingly conducting some sort of lifelong invisibility experiment by steadfastly refusing to illuminate, even (or especially) if they’re in a grey car, and it’s dusk, foggy and raining. – Yours, etc,