I think that the authorities want to ban the niqab, the black cloth of face covering, which they ignorantly confusing with the hijab and burka.
However, they haven't got the courage to single out Muslims, so to be inclusive they must ban other religious symbols too.
I agree that the cross is also a religious symbol and excluding it is hypocritical.
Wearing the kippah nowadays at least in Europe with the Muslim population at large is unwise, inviting all sorts of problems.