Ok, lets see if I can't make myself unpopular with everyone on this subject. My apologies to everyone in advance.
I'm going to attempt to first establish some theological principles and then move to actual practice.
First Christians are commanded in Scripture to obey the laws of the civil magistrate and the authorities above them if they are:
A) Consistent with the Commands of God - An example would be laws forbidding murder or theft, God has already commanded these things in the bible.
B) Matters of Indifference - Examples would be speed limits, no dogs allowed signs, or typical school uniforms
The only time they are allowed to disobey lawful authorities are if the commands of that authority would go against the commands of God, so for instance when the Apostles were commanded by the Sanhedrin (the Jewish Ruling Council) not to teach and preach in the name of Jesus Christ, their answer in this matter was
"We ought to obey God rather than men." (Acts 5:29) Similarly when Christians are forbidden to gather for worship, read the Bible, preach and teach the Christian faith, and so on these are laws they must disobey. Less obvious examples of laws that must be disobeyed would be laws like the Nazi laws to identify and turn in Jews, mandatory abortion laws (like China's), and the like.
Now, there is no command in the word for Christians to create and wear religious symbols. And while I hate to disagree with AKIron, even the Star of David is not found in Scripture. The Apostles did not teach or use religious symbols, icons, paintings, or jewelery and the only commanded visual symbols one finds in the NT are the water of baptism and the bread and wine of the Lord's Supper. The use of religious signs in Christianity began to show up in the late 1st and early 2nd century (the fish (ICTHUS), anchor, cross, etc.), actual pictures didn't come in until much later.
In any event, is there a biblical command to wear symbolic jewelery, use icons, etc? Not at all. I have never worn nor used crosses, etc. I do however have a little Icthus on my car - but that's more of a reminder to me to try to be a humble a courteous driver. Would I say that crosses are prohibited? No, they are something indifferent.
Now while chastity before marriage
is a command in the Bible, wearing a "chastity ring" is not. Millions of Christians have managed to keep the command without wearing a ring (and I'm sorry Chair, I know plenty of Christians who were actually virgins when they got married) and we no more need to wear a ring to remind us than I need to wear a T-shirt with an X-over a boxing glove to remind me not to brawl. If I want to wear such a shirt or a ring, I may of course do so, but it is no different from any other religiously themed clothing or jewelery. It is not required, commanded, or "holy".
Now the school has a no jewelery policy in keeping with their uniform and it is well within their rights to enact such a policy. These silver rings are religiously themed jewelery, no more and no less. They are therefore subject to the ban. Since they are something indifferent, the girl and her family should have accepted the ban. Had the school banned her from carrying a bible to read during breaks, that would have been a different matter. I would have told my own child she could not wear the ring to school.
As for the other religious garb, Islam does state that all women must keep their hair covered. Only "Kuffars" who disobey the law of Allah have uncovered hair, therefore it is a required piece of garb. Likewise, no observant Sikh uncovers his hair in public so the turban is necessary. While I disagree with their theology, I agree that if they wish to observe their religion they must wear the Hijab and the Turban.
Personally, I am weary of the fads and the influx of "Jesus junk" into the Christian faith. The typical Christian "book store" is beginning to look more like a medieval relic shop for gullible pilgrims and the fact that most of these modern-day plastic "aids to faith" are made in China - a nation that suppresses and persecutes Christians - should cause us nothing but embarrassment. Once again we seem to be placing symbolism over revelation. Its not a good sign when every evangelical kid has a What Would Jesus Do bracelet, but is blissfully unaware of what Jesus actually did and commanded. This might be part of the reason that the SBC estimated that 88% of them leave the faith in College.
Anyway that's my .02 cents.
Night all. Have a good Lord's Day.

- SEAGOON