The Supreme Court has held that individuals who sign a petition may not keep their identity private–disclosing that information does not generally violate the First Amendment. At issue before the Court was a petition signed by voters in Washington state. The State had passed a law that expanded domestic partner rights, and it was met by resistance, and 120,000 individuals signed a measure asking voters to repeal the new law. That measure was defeated by voters.
Nevertheless, individuals who had signed the repeal measure sought to protect their identities, worried that disclosure may lead to harassment. The Court held that disclosing the name, however, does not generally violate the First Amendment. The judges did say that there are privacy exceptions, and asked that the lower court consider the applicability here.