I think protestors should adopt a uniform of wearing a high-visibility vest and hard hat because they are supposed to be there and are just doing safety checks.
Actually, a maximally confusing thought (and illegal if they did it) would be for all the protesters to show up in high quality police uniforms. Though things like piercings, tats, and hair styles would be giveaways that some of them weren't cops. The police would throw everything could at them if they did that though.
Probably illegal. And certainly a good way to get your ass kicked by protesters (and the police).
It is illegal. In California, it’s covered under Penal Code §538d[0]. In short, it’s not illegal to wear a police uniform, but doing so with the intent to deceive anyone (actual officers included) is illegal.