A pupil posed this question yesterday ... the first time I've been asked it in six years. And what a good one ! Laws affecting other walks of life change quite often these days. How about when driving?
Well, I saw the above sign in Nottingham last year. It combines "Diagram 557" (from local authorities' guide to traffic signs) and the icon for cycles. It makes sense. But I can't find it in The Highway Code, companion publication Know Your Traffic Signs, or the relevant law. (Plus, I was interested to find that "slippery road" comes in the section of signs ONLY to be used as temporary warnings ... but often seen permanently sited).
I await reply from Nottingham City Council. And shouldn't a sign also warn scooters about the slippery rails of on-road trams ?