As a libertarian, ie someone who believes people should be free to do as they like so long as it doesn't physically harm anybody else, then yes, religious symbols should be allowed into the workplace. I've never understood why certain companies disallow their employees to wear cross necklaces, although I'm reassured that such incidents are isolated.
People should be allowed to wear crosses, turbans, hijabs, rosary beads, kippah etc. The only exception I can think of is the niqab, but if you're stupid enough to wear that, you're unlikely to have a job in the first place.