Sikh have no obligation to wear the turban they do so as a tradition and because of practicality.

The hijab isn't an obligation it's a choice made by women when old enough (when they get to make the choice and not something forced upon them by society), many women don't wear it.

Not all Jews wear the yarmulke either.

The ban applies to Christians who want to show the cross they wear around their neck too or if you want to go with more obvious symbols then nuns have been out of our public schools for decades because the state kicked them out, yet you won't hear anyone against Bill 21 taking about how we should let priests and nuns be teachers again!

It might be a symbol of your faith but we decided long ago that in Quebec your faith is a private matter and many immigrants agree with that because they know what life is under a religious state (implied or not).