Bradman Museum director Richard Mulvaney said the pre-eminence of Sir Donald as a cricketer as well as his generosity in responding to requests for his signature had made Bradman memorabilia a target for misrepresentation and forgeries.

"It's common for many sportsmen - particularly cricketers - to be asked for their autographs and Sir Donald Bradman was particularly generous in this area, right up to his death," said Mr Mulvaney.

"He was probably the most prolific letter writer and receiver you could think of and this set him apart from other cricketers."

After the Bradman Museum was established, Sir Donald signed over the rights for the use of his name and signature to generate an income for the Bradman Museum.

However, Sir Donald continued to respond to requests for autographs and signed items, unwilling to disappoint admirers.

"It is almost impossible to differentiate the fans from the rogues, so Sir Donald felt he had no choice but to continue to sign items," Mr Mulvaney said.

"Because of Sir Donald's propensity to sign letters on request, a lot of people have got Sir Donald Bradman's signature and some have turned it into products to make a profit without our consent or Sir Donald Bradman's consent.