BEIJING — If it had happened elsewhere, it might have been dismissed as a teenage prank.
A couple of 15-year-olds last year hung a Tibetan banner on the wall of their classroom next to portraits of Mao Tse-tung and Deng Xiaoping. They drew Xs over the faces of the former Chinese leaders and scrawled "Long Live the Dalai Lama" on the wall.
But in China, the incident was taken dead seriously. Three boys who attend a Tibetan school in Sichuan province were arrested, and one of them, who confessed to being the ringleader, was held and interrogated for a month.
This year, the 50th anniversary of the Dalai Lama's exile to India, the boy is under virtual house arrest -- by his own parents.
"They want to make sure he doesn't do anything like that again. They don't want him to get arrested again or hurt," said a relative, who asked not to be quoted by name.
As the traditional season for protests against Chinese rule begins, many of China's 2.8 million Tibetans are in a similar quandary. As sure as the melting of the snow on the Tibetan plateau, protests erupt about this time of year as Tibetans mark the anniversary of a failed uprising that began March 10, 1959, and led to their spiritual leader's exile. But with the special anniversary this year, the Chinese have taken extraordinary security measures, hoping to prevent a recurrence of last year's protests, the most violent in decades.
Exact numbers are difficult to come by in China, but residents of the Tibetan areas say that tens of thousands of paramilitary troops have been deployed. Telephones are tapped; cellphones and Internet connections disrupted.
Foreigners are barred from entering not only the Tibetan autonomous region, but heavily Tibetan areas in Qinghai, Sichuan and Gansu provinces.
The mountain roads leading into Tibetan villages are clogged with armored personnel carriers and buses filled with riot police.
The security forces make their presence felt by cruising up and down main streets, or conducting training in as public a way as possible.
"They made a picture of a man and are using it for target practice. They do it to scare us," said Tashi, a 20-year-old student from Ganzi (known to Tibetans as Kardze), in Sichuan province.
Like many Tibetans, Tashi refuses to be identified by anything other than a first name for fear of retaliation for speaking out.
In Lhasa, the Tibetan capital, security cameras are ubiquitous.
"You feel like you're being watched all the time. It feels very uncomfortable," said Tsering, a 38-year-old Tibetan construction worker from Lhasa, who left late last year.
Tibetans say they would like to do something to commemorate the victims of last year's violence, who they say number more than 200. (The Chinese counter that 21 died and that most were Chinese.)
"We would like to do a candlelight demonstration for the people who died, but we are afraid. So we will keep silent," said Tashi.
But to demonstrate or not has become a subject of great debate among young Tibetans.
"Our teachers have told us not to be stupid and talk about freedom," said a 19-year-old student from Tongren, a monastery town also known as Repkong, in Qinghai province, that has been a hotbed of ethnic unrest.
"Everybody is afraid. There are armed police all over our town," he said.
The problem for Tibetans is that the Chinese treat any expression of Tibetan identity -- even waving a flag or posting a portrait of the Dalai Lama -- as criminal activity.
Human Rights Watch on Monday issued a detailed report saying that China had arrested thousands of Tibetans on the vaguest of charges, failing to disclose what crimes had been committed or where people were being held.
And today, the Dalai Lama launched his own harsh criticism of China, telling thousands of supporters in Dharmsala, India, that Chinese rule has created a "hell on earth," the Associated Press reported.
Martial law and hard-line policies such as the Cultural Revolution, he said, have "thrust Tibetans into such depths of suffering and hardship that they literally experienced hell on earth. The immediate result of these campaigns was the deaths of hundreds of thousands of Tibetans."
Tibetan culture and identity are "nearing extinction," he told about 2,000 people, including Buddhist monks, Tibetan schoolchildren and a handful of foreign supporters.
Although his comments were unusually strong for a man known for his deeply pacifist beliefs, he also urged that any change come peacefully and reiterated his support for the "Middle Way," which calls for significant Tibetan autonomy under Chinese rule.
"I have no doubt that the justice of Tibetan cause will prevail if we continue to tread a path of truth and nonviolence," he said.
After his speech, thousands of young Tibetans took to the streets of Dharmsala chanting, "China Out!" and "Tibet belongs to Tibetans!"
Protests also erupted outside the Chinese embassies of South Korea and Australia.