Yes, I believe that it is already illegal. It's a way of promoting hate or advocating genocide.
However, as someone who's working on the front lines with law enforcement every day on individual hate crimes that take place, I will tell you that police are very reluctant to consider it a hate crime. Just seeing the symbol, they're very reluctant to investigate; they're reluctant to lay charges. They don't know whether charges will stand up in court. For that reason, I do believe that it would be an advancement to make the law more explicit so that there was less ambiguity in the eyes of law enforcement.