I'd be none to happy. To ask me as a Jewish male to remove my wooly hat, but to not ask a Sikh to remove their turban is discriminatory.
In any case, its a joke, a pointless exercise. It's about as effective as a sign reading "Armed robbers - please leave shotguns outside". The only people likely to comply are those who are likely to behave themsrlves anyway.
In any case, id not remove it in the basis there's not a lot they can do. He ain't gonna pick me up and carry me out, he can call the police but they've got no routine powers to eject people from private property. I'd just select my goods, pay at the self service till, and be on my way and there's not much can be done to alter that course of events.