Three Hong Kong judges will rule on Tuesday whether the protest slogan "Liberate Hong Kong. Revolution of our Times" is a call for secession when they deliver a verdict on charges against a man arrested at a demonstration last year.

The landmark ruling could have long-term implications for how a national security law that China imposed on its freest city a year ago against secession, terrorism, subversion and collusion with foreign forces reshapes its common law traditions, some legal scholars say.

Activists say a ruling to outlaw the slogan will tighten limits on free speech.