Of course they are banned. There is a long list with organisations and groups that were banned since 1951. https://de.wikipedia.org/wiki/Liste_in_Deutschland_verbotener_rechtsextremer_Organisationen
Not only symbols are prohibited. Extreme-Right / Facist / Nazis writings, music, images, videos, etc. are also banned.
Holocaust denial is forbidden. Historical relativism in relation to the Second World War is prohibited. etc.
Admittedly, it is not enforced often enough and hard enough, but in general this falls under criminal organisations law.