Approaching this from the logical end of things:
If a protest requires your personal info, you should not go.
No protest needs you that much that they need your name/email/address/etc. Those are the ones with a potential to devolve into violence. If they weren't facing a potential of violence, they wouldn't be asking for personal information of POTENTIAL SCAPEGOATS. No troublemaker is going to sign their info onto an attendance list when they have plans to cause problems.
If you happen to have business in the area, that's one thing. Just keep your eyes open for shenanigans and don't get involved in violence or whatever. Be good, and above all, be safe.