BEIJING: The tough guys wore smiley face stickers, but they weren't there to spread good cheer.

Scenes of pushing, shouting and shoving outside a Beijing courthouse this week were orchestrated by plainclothes security officers identified by a sticker familiar around the world — the yellow decal identified since the 1970s with the slogan "Have a Nice Day."

Their attempts to intimidate journalists, foreign diplomats and a small cohort of human rights advocates outside the trial of a well-known activist lawyer are all-too familiar to China's beleaguered dissident community.

"The plainclothes police are the ones the Communist Party uses when they know what they're doing has no basis in law," said independent environmental activist Wu Lihong, who lives under a form of house arrest that becomes especially strict during sensitive political occasions.

The use of such agents dovetails with the party's desire to pay lip service to the rule by law while quashing all opposition, controlling the public discourse and sentencing critics to lengthy prison terms for hazily defined national security crimes.

The plainclothes agents did not specifically identify themselves as such, but foreign journalists in Beijing have interacted with them for two decades. They typically appear in civilian clothes in a wide variety of circumstances where foreign media might interact with government critics and authorities want to maintain control without uniformed officers intervening directly.

That was on full display Monday outside Beijing's No. 2 Intermediate Court, where lawyer Pu Zhiqiang was on trial on charges of provoking trouble and stirring ethnic hatred with online commentary critical of one-party rule.

Dozens of journalists were pushed around, including one who was slammed to the ground. At least five protesters were assaulted and taken away in vehicles, while diplomats from the European Union and the United States were interrupted, cursed at and jostled while attempting to read out statements criticising Beijing's actions.

The smiley face stickers were presumably meant to identify the plainclothes officers to their uniformed colleagues and other security agents. Similarly, plainclothes agents wore green stickers last year to identify themselves while breaking up protests outside the Beijing courthouse where clean government advocate Xu Zhiyong was tried on charges of gathering a crowd to disturb public order.

Xu, founder of the grassroots New Citizens movement, received a four-year sentence. Pu has denied the charges against him and the trial concluded about midday, with his lawyer Shang Baojun saying a verdict and sentence would be delivered at a later date.

As is standard in such cases, the officers on Monday refused to display identification and wore anti-smog face masks to obscure their identities.

Using such anonymous agents, or even independent contractors without official status, offers the government plausible deniability in the event situations might turn nasty. It also allows a degree of flexibility and a buffer between the authorities and actions that might be distasteful or illegal, while permitting uniformed officers to appear reasonable and law-abiding.

At least on Monday, the tactic may have backfired. Images broadcast around the world showed a violent and chaotic scene and drew even-more attention to the case of the lawyer Pu, who is being prosecuted for his past work advocating for political dissidents and government critics including avant-garde artist Ai Weiwei.

The scuffles attracted passers-by and about 50 people gathered and shouted slogans, including "Pu Zhiqiang is innocent." Signs displayed were emblazoned with slogans such as, "The people don't even have the rights that dogs enjoy," while plainclothes officers shouted back abuse, including calling the protesters "traitors."

Whether China's image-makers care about the impressions such scenes create is doubtful. Beijing has consistently rejected foreign pressure over its domestic politics, while president and Communist Party chief Xi Jinping stridently asserts that China will never compromise on core issues of sovereignty and independence.

"For the authorities, it looks like disastrous public relations, but maybe they just don't care," said Jean-Pierre Cabestan, an expert on Chinese politics at Hong Kong Baptist University. "They can always claim that (the officers) were ordinary citizens and there's very little anyone can do."

The ministry that oversees China's domestic security services did not immediately respond to faxed questions about the deployment and supervision of plainclothes officers.

Plainclothes officers and police auxiliaries are deployed for both short- and long-term assignments involving duties that fall outside the strict purview of uniformed officers. In one of the best-known cases, informal law enforcement officers were entrusted with guarding the rural home of blind legal activist Chen Guangcheng, who nevertheless escaped their around-the-clock watch to seek shelter at the US Embassy in Beijing.

Plainclothes officers are also assigned to watch the apartment of Liu Xia, the wife of imprisoned Nobel Peace Prize laureate Liu Xiaobo, who lives under virtual house arrest in central Beijing. Criticism from the outside only seems to embolden decision-makers in the government that now spends more each year on domestic security than it does on national defense.

"They are simply forcing others to accept their will and showing that they will never accept outside sanctions on China's human rights situation," Cabestan said.