This, ultimately, is a virtually pointless debate because it would be easy to ban the Hells Angels from wearing their badges in public. However, if they remove their badges, you still have to prove that they're members of a criminal organization in any case. The mafia doesn't have a uniform, and its members are very effective, even more than the Hells Angels in many cases.
Ultimately it's a waste of time to want to do that, or else do it, but let's also think of other ways to be more effective, because, if the Hells Angels can no longer wear their colours, they'll continue their criminal activities in any case. And that's the problem; it's not the public display.