JOHANNESBURG — The sign-language interpreter on stage at Nelson Mandela’s globally broadcast memorial service was a faker who was waving his arms around meaninglessly, advocates for the deaf said Wednesday.

The allegation raised questions about how and why he managed to insert himself into a supposedly secure event attended by scores of heads of state, including President Obama.

As one world leader after another took the stage in a gigantic soccer stadium to pay homage to Mandela, the unidentified man at arm’s reach from them appeared to interpret for the deaf. But four sign language experts told The Associated Press that the man was not signing in South African or American sign languages and could not have been signing in any other known sign language because there was no structure to his arm and hand movements.

Bogus sign language interpreters are a problem in South Africa because people who know some signs, often because they have deaf relatives, try to pass themselves off as interpreters, said Ingrid Parkin, principal of the St. Vincent School for the Deaf in Johannesburg. And those who hire them usually don’t know how to sign, so they have no idea if the people are qualified, she said.

“They advertise themselves as interpreters because they know 10 signs and they can make some quick money,” Parkin said. “They are taking advantage of the deaf community to make money.”

In Washington, White House spokesman Josh Earnest said he was unaware of any security concerns related to the fake interpreter.