Oh, great. Make them stand out to jihadis who hate them even more than other kafirs.
It seems to be optional, not required
I assure you they are quite tranquil about the risks, whether it be an increased conspicuity to jihadis, the chance of being mistaken for a jihadi by a redneck yokel, or the inability to wear a helmet or gas mask properly. Their bravery and loyalty have earned them a lot of slack on their religious garb, in my view. If all immigrants were Sikhs we'd have essentially no trouble at all with immigration.
Do you know the main reason the turban is so sacred to them? They WANT to stand out in a crowd, because the principles of their faith require them to protect the weak and downtrodden. A woman who is being attacked or stalked can run to a Sikh and beg for his protection, and his faith requires him to defend her even if it costs him his own life.