You're going to think I'm really pedantic, but in most shops I go into it says 'Masks must be worn.' Some do say face-coverings, I admit.
To me, a face covering could be anything from something some Muslim women wear for cultural or religious purposes, to a buff pulled up to the nose when entering a shop, or a scarf, right down to masks of various qualities — fabric, FFP2s etc. Having grown wise to the ways on online shopping over the last two years, I've learned to be really specific.