Faced with a barrage of campaigns on issues such as Tibet, press freedom and Darfur, China's communist rulers are mounting a massive security clampdown ahead of next month's Games, saying they will tolerate no dissent of any kind.

Organisers have invoked the Olympic Charter, the rulebook drawn up by the International Olympic Committee, for overseeing the Games, which forbids any form of "demonstration or political, religious or racial propaganda" from athletes.

However groups are coming up with an array of ways to get around the rules in the hope of creating a moment similar to when black American sprinters Tommie Smith and John Carlos famously raised their black glove covered fists at the 1968 Mexico Games.

Pro-Tibetan activists are urging athletes at the Olympics to make a simple T hand signal to indicate support for the Tibetan cause.

European activists are planning to wear orange as a human rights protest while other groups say they ask athletes to wear sport wrist-bands or find different ways to express their political positions at the Games.

The T sign, similar to the coach's time-out signal in a basketball game, is an easy-to-perform gesture that could become an effective symbol of protest at the Games, according to the London-based Free Tibet Campaign.

"Now all we need are some brave athletes who are willing to show they care about human rights by making the T sign in Beijing," Anne Holmes, acting director of the group, said on the website www.tfortibet.org.

Beijing has come under international criticism for staging a crackdown on pro-Tibetan protests in the Himalayan territory in March, which exile groups claim has left more than 200 people dead.

Other groups using symbols to dodge tight Olympic security include Team Darfur, a group of more than 360 past and current athletes from 49 countries dedicated to ending the bloodshed in Darfur.

China, a close ally of the Khartoum government, has come under international criticism for not doing more to stop civil conflict in the western Sudanese region of Darfur.

Members of Team Darfur who will compete in the Beijing Olympics and Paralympics will be identifiable from their distinctive, green and black sweatbands.

They will also sport special wrist-bands, "to show the world that the world's athletes will act as one to fight for the protection of the people of Darfur," according to the group's website.

Another activist group has urged US President George W Bush to wear a wrist-band highlighting the fate of North Korean refugees in China.

Bush has said he will attend the August 8 Games opening ceremony and the US-based North Korean Freedom Coalition asked him in a letter last month to wear the wrist-band to show solidarity with the refugees.

Up to 300,000 North Koreans are believed to have fled to China, which terms them economic migrants and hunts them down for repatriation. Some face execution on their return home, according to reports.

On human rights, European activists say they have found a simple way of getting their message out despite heavy security in Beijing.

Set up by Danish sculptor Jens Galschiot, a group called The Color Orange is urging athletes and spectators to wear "anything orange" during the Games as a symbol of protests against China record on human rights.