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.

The slogan was chanted during pro-democracy protests, posted online, scrawled on walls and printed on everything from pamphlets, books, stickers and T-shirts to coffee mugs.

During the 15-day trial of 24-year-old waiter Tong Ying-kit, the court heard how he rode a motorcycle, carrying a black flag bearing the slogan into several riot police in central Hong Kong on July 1 last year.

Tong was the first person charged under the national security law.

Lead government prosecutor Anthony Chau argued in court that this was a terrorist act, and that Tong had sought to incite people to secession, both "grave" offences under the security law that could bring prison terms of several years to life, if convicted.

Tong has pleaded not guilty to charges of terrorism, incitement to commit secession and dangerous driving causing grievous bodily harm. Chau did not respond to requests for comment. Defence barrister Clive Grossman declined to comment.

A cornerstone of the trial has been the prosecution's argument that slogan "connotes Hong Kong independence" - a position unacceptable to China, which considers the financial hub and former British colony an "inalienable" part of its territory.

During the protests that began in 2019 and paralysed the city, millions took to the streets to oppose a perceived clampdown by China's Communist Party leaders on the city's constitutionally enshrined freedoms. The slogan was ubiquitous.

When Hong Kong returned from British to Chinese rule in 1997, China's Communist Party leadership pledged to allow the city to maintain its judicial system and retain a wide degree of autonomy and freedoms as part of a binding deal with Britain.

Critics say those freedoms are being trampled, an assertion authorities in Beijing and Hong Kong reject.

Separatist or activist?

In the court hearing, the meaning of the slogan was fiercely debated in exchanges that drew on eclectic references to Chinese emperors, Marxism-Leninism, the ancient Chinese poet Li Bai, Malcolm X, rampaging Mongol barbarians, and former nationalist leader Chiang Kai-shek.

The prosecution told the court the slogan was coined in 2016 by Hong Kong activist Edward Leung, a well-known advocate for Hong Kong independence. Leung is serving a six-year jail term for rioting and could not be reached for comment. There was no immediate comment from two lawyers who represented him.

An expert witness for the prosecution, history professor Lau Chi-pang, testified that the first portion of the Chinese slogan, translated as "liberate", or "reclaim", had been used throughout Chinese history from the Qin to the Qing dynasties, and that the meaning, to recover lost territory or to expel an enemy "has not changed throughout a thousand years".

Lau told the court the words in the slogan, taken alone, or separately, could have but one meaning: "They related to separating the Hong Kong Special Administrative Region from the People's Republic of China."

Lau also referred to a rally on July 21, 2019, when protesters, who chanted the slogan, damaged a national emblem outside China's representative Liaison Office in Hong Kong. The conduct and use of the slogan that day had "the objective of rejecting the governance of the People’s Republic of China", the prosecution told the court.

Lau declined to comment.

Tong declined to stand as a witness. The defence called two academics, political science professor Eliza Lee and Francis Lee, a professor and expert in political communication. They are not related.

In a report drawing on hundreds of interviews with protesters on site and over the phone, as well as a statistical analysis of more than 25 million online posts, Francis Lee said there was "no substantial linkage" or correlation between the slogan and independence, as maintained by Lau.

"The subject slogan was understood, really, by many people in many different ways," Francis Lee told the court.

Eliza Lee told the court the slogan was meant to “unite freedom-loving people of all ages”. She accepted, however, that it could have pro-independence connotations to some people.

Eliza Lee did not respond to a request for comment. Francis Lee declined to comment.

At one point prosecutor Chau sought to draw parallels between Edward Leung and the U.S. civil rights leader Malcolm X, asking Eliza Lee whether she would consider him to be a separatist?

"How much do we need to venture into the complicated history of racial segregation in order to understand this," Lee answered, before one judge, Anthea Pang, interjected.

"Whether Malcolm X was or could be regarded as a secessionist or separatist is a question far far removed from the issues presented in front of the court."

In his closing speech on Tuesday, Grossman said protesters worldwide often held up signs without facing prosecution, and that Tong should be acquitted if the meaning of the slogan was open-ended.

Grossman said Lau had an "untenable, rigid, mechanical view of history" that paid no heed to rhetoric, and the meaning of the slogan could not be pinned down as Lau was trying to do.

Pang said the court would consider whether the "natural and reasonable effect" of the slogan could indeed incite others to secession, as well as Tong's criminal intent, in making its ruling.