The Mishnah on Amulets on the Sabbath

Hebrew

6:2. A man may not go out [on the Sabbath] with nail-studded sandals, nor with a single [sandal] unless he has a wound on [the other] foot. A [man may not go out] with phylacteries [tefillin], nor with an amulet unless it [was written] by an expert, nor with a cuirass, nor with a helmet, nor with greaves. [ . . . ]

9. Boys may go out with their knots, and princes with bells. So [indeed] may anyone, but the sages speak of the present [or, common custom].

10. One may go out with a locust egg, or with a fox’s tooth, or with the nail of one who has been hanged for the sake of remedies—these are the words of R. Meir. However, the sages say: This is forbidden even on a weekday because [it imitates] the ways of the Amorites.