A Rosary is not jewelry and should not be worn about the neck as a necklace. It should be carried in the pocket and be brought out for prayers and then returned to the pocket.
Correct, this is not Catholic practice to wear the rosary outside, as jewelry.
But in a more general 1st Amd, sense, it is protected religious “speech.” Criminy, we now have Sikhs in the Army wearing bloody turbans.
So no way can the Official State Atheism Board rule out wearing a rosary. Unless the hijabs and turbans etc go as well.