A fake sign language interpreter took to the stage during yesterday's memorial in South Africa for the late Nelson Mandela, outraging deaf people across the world.

Deaf SA, South Africa's leading deaf association, condemned the presence of the unknown man, who gesticulated gibberish before a global audience of millions 

The event was attended by South African President Jacob Zuma and scores of world leaders, including US President Barack Obama.

While dignitaries were addressing the crowd in the 95,000-seat Soccer City stadium, the man, with an official security pass around his neck, produced a series of hand signals that experts said meant absolutely nothing.

"He was basically gesturing. He didn't follow any of the grammatical rules and structure of the language. He just invented his signs as he went along," said Delphin Hlungwane, an official South African sign language interpreter at Deaf SA.

"There was zero percent accuracy. He couldn't even get the basics right. He couldn't even say thank you," she said.           

Ms Hlungwane said the "interpreter" also failed to impart to television viewers - as he should have done - that the crowd gave a hostile reception to President Zuma, a scandal-plagued leader who faces an election in less than six months.

"You're supposed to indicate with your facial expressions, even if it's not an exact sign," she said.

"He didn't indicate that at all. It just passed him by."

The hunt is on for the mystery man.

"Nobody knows who he is. Even at this hour, we still don't have his name," Ms Hlungwane said.