The Electronic Frontier Foundation's Digital Security Tips for Protesters builds on its indispensable Surveillance Self Defense guide for protesters with legal and technical suggestions to protect your rights, your data, and your identity when protesting.
Some of the measures are obvious in hindsight, like walking or cycling to protests to avoid automated license-plate readers and transit logs that can be use to log the identities of all the protesters at an event; others are more subtle, like removing fingerprint unlock from your devices because you can be physically forced to put your finger on the reader (and this may or may not be legal), but it's a lot harder to get you to disclose the secret passphrase to unlock your phone.
#10: Organizers: consider alternatives to Facebook and Twitter
Facebook and Twitter provide a large user base for you to promote your cause, but these popular social media platforms also carry risks. Viewing an event page, commenting on the event, and stating your intention to attend are all actions viewable by law enforcement if the pages and posts are public, and sometimes even if the pages aren't (subject to a court order). For actions that require a more cautious approach, consider forming a group chat via Signal as described above.
[Bill Buddington/Electronic Frontier Foundation]