A tough question that I have been wrestling with off and on all day. A possible legal avenue to ban them would be similar to what Germany did, they are symbols, not speech. Additionally, those symbols represent an enemy and belief system that declared an unprovoked war on us, sought our complete subjugation, the end of our way of life, and the destruction of the very Constitution now protecting those hideous symbols. Any symbols that meet those criteria I think could reach a non-protected 1st amendment threshold and be banned.

The Alien and Sedition acts could be a basis for banning the symbols:  https://en.wikipedia.org/wiki/Alien_and_Sedition_Acts

As well as the following acts:
Alien Act of 1705 in Great Britain
Civil Liberties Act of 1988
Espionage Act of 1917
Logan Act of 1799
Nullification Crisis
Sedition Act of 1918
Alien Registration Act of 1940
USA PATRIOT Act of 2001
Violent Radicalization and Homegrown Terrorism Prevention Act of 2007

Where is a good lawyer when needed?