Found a description , don't know if it is accurate .
Raf Doctor, Lettering, Patch For Yellow Warning Jacket, Reflective, 100x300mm
https://www.ebay.co.uk/itm/152902920...6&toolid=10001
Edit : Have seen similar 'reflective' badges for High-Vis jackets , can be sewn on or slotted into clear breast pocket.
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