I’ve been a public school teacher. I don’t think any of my students or their families were actually Satanists, but you can bet some kids (high school) thought it was fun to say or bring all kinds of horrible things to school.
I would consult the student handbook. If religious symbols are banned at school, then I would follow the proper procedures.
If, like most schools my son attended, religious symbols are permitted, I would do nothing (as I would for the Christian who wore a cross, the Jewish student who wore a star of David, etc.)
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.