www.independent.co.uk/news/world/europe/french-school-forces-muslim-and-jewish-pupils-to-wear-coloured-discs-a6669396.html
So basically it stops dc being given food they can't have at lunchtime and no way imo can it be compared to the yellow star.
I might be biased in that I am a school cook and before that a nursery cook where every dc had a placemat with their photo and dietary preference. Schools don't do this instead we have a list with photos on and what they can't have but we have had near misses with jelly for example. A child who couldn't have the jelly asked for the jelly knowing they couldn't have the jelly and luckily as soon as the server put the jelly on the plate the child said but I'm not allowed this it's not halal and she had a fresh new plate of food.
Something for the cooks to see in primary schools to avoid mix ups is a great idea. The only problem I see with what the French have done is not to do it for all dietary requirements like allergies and intolerances