If you are detained and questioned by police, you have a right to remain silent, and to speak with an attorney before and during any questioning. It is best to say “I want my attorney and I choose to remain silent” and then refuse to answer questions until you have a chance to talk to a lawyer.

It should be noted that failure to identify does not fall within your right to remain silent. You will be arrested if you don't ID yourself with name and DOB. They have to be able to figure out if you're wanted to conduct their investigation. But that's the most that is required and you should probably shut up after that.

Don’t bring anything with a modem and you’re good to go.

Some of this is good advice but I recommend evaluating every protest, having a real plan for transportation and a buddy system, and trying to be as secure as possible by default and only making exceptions when necessary.

Most of the guide is about phones and how they can leak information. The only surefire way to prevent your phone from leaking location information to show you were at a protest is to leave it at home. That should be your default. The next option is to use a burner, but you must be very careful about when you charge your burner and turn it on, as you never want it to be on near where you live or work. Cell signals can be triangulated to a few block radius. The next option is put your phone in airplane mode and turn it off. Your phone is now an emergency device, you won't turn it in at the protest unless a safety critical situation develops, such as being separated from your group by police or other right wing violence. Under no circumstances should you use your main phone to coordinate day-of at any event. If you are an organizer, use a burner to do this. This is also a reason to not use Signal for day-of coordination, as it will pressure you to either turn your burner on at home so that you can coordinate or associate your signal account with other devices traceable to your home or work. Walky talkies are best but Signal alternatives like davel suggested are also better.

Also, cover your face and wear sunglasses.

Why not Signal? » Good Alternatives

Should really be prefaced by: Don't bring your phone. Write the phone number you plan to call if arrested on your lower arm in sharpie. If for some reason you have to bring your phone, read the following.