It might be.
Some states have laws about releasing the ID of an informant, because it puts them in danger.
There can be certain restrictions on the First Amendment.
Google Justice Holmes and his opinions, including about yelling Fire in a crowded theater. In fact there's an excellent, relatively new book analyzing Holmes's First Amendment jurisprudence. That could also be an good way to occupy your time.
www.court-martial.com; www.court-martial.us.com; firstname.lastname@example.org 703-298-9562, 800-401-1583. Answering your question does not create an attorney-client relationship.
Legal? Criminally or from a civil point of view?
First impression is it is an exercise of free speech.
Second thought, what about the possibility of endangering someone's life?
There mmay also be lawfull restrictions on your ability to parade around with a sign.
Bottom line, is there are better ways to address the "problem". Especially so if you are connected to the defendant. There are disuading witness laws in this state.
The above is not intended as legal advice. The response does not constitute the creation of an attorney client relationship as this forum does not provide for a confidential communication.
Next month you will be posting on Avvo about how the cops are harassing you for no good reason. This will be the reason.
My responses to questions on Avvo are never intended as legal advice and must not be relied upon as legal advice. I give legal advice only in the course of an attorney-client relationship. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. That relationship is established only by individual consultation and execution of a written agreement for legal services.