By Ed Cropley JOHANNESBURG (Reuters) - A fake sign language interpreter took to the stage during a mass memorial for anti-apartheid leader Nelson Mandela, gesticulating gibberish before a global audience of millions and outraging deaf people across the world. DeafSA, South Africa's leading deaf association, condemned the presence of the unknown man at the memorial, which was attended by President Jacob Zuma and scores of world leaders including U.S. President Barack Obama. While dignitaries were addressing the crowd in the 95,000-seat Soccer City stadium, the young, suited man with an official security pass round his neck produced a series of hand signals that experts said meant absolutely nothing. Besides the bizarre twist to an event that also saw Zuma booed and jeered, the man's presence on the stage within yards of Obama and Brazil's Dilma Rousseff raised awkward security questions. "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 sign language interpreter at DeafSA. "There was zero percent accuracy. He couldn't even get the basics right. He couldn't even say 'thank you'," she told Reuters. Hlungwane said the fake interpreter also failed to impart to television viewers - as he should have done - that the crowd gave a hostile reception to 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." In Britain, the Action on Hearing Loss group said as a result of the fake mimer's actions, "deaf or hard of hearing people across the world were completely excluded from one of the biggest events in recent history." MAN-HUNT The revelations have sparked a man-hunt for the mystery mimer, who is totally unknown to South Africa's deaf community. The government, which was officially in charge of Tuesday's ceremony, said it had tried and failed to get to the bottom of the matter. "Government is looking in to this matter but has not been able to conclude this inquiry due to the demanding schedule of organising events," Presidency Minister Collins Chabane told a news conference. Zuma spokesman Mac Maharaj said he was checking the reports, while the SABC state broadcaster, which covered the memorial, said it was not involved as it had its own on-screen signers. The ruling African National Congress (ANC) also professed no knowledge, even though several television clips from a big party meeting a year ago showed the same man gesticulating on stage alongside Zuma. "I don't know this guy. He doesn't work for the ANC. It was a government event. Ask them," spokesman Jackson Mthembu said.