Entrepreneur Dick Smith is offering a $5,000 reward for information leading to who created the infamous Marree Man artwork 20 years ago.

Key points: Marree Man drawn in SA desert in 1998

Marree Man drawn in SA desert in 1998 Clues sent via fax suggest Americans with military connections

Clues sent via fax suggest Americans with military connections Dick Smith offers $5,000 reward for who did it

He has been investigating who created the three-kilometre-tall etch in the desert about 600km north of Adelaide.

Despite many clues and leads, he is no closer to finding out its creator.

Suggestions Mr Smith has researched include rumours it was created by late Alice Springs artist Bardius Goldberg, by local Indigenous people, by Americans and by the Australian Army.

"There's been so many different claims and the only one I don't believe in is that it was done from outer space," Mr Smith told ABC Radio Adelaide.

When the artwork appeared in 1998, accurate GPS was not available to the public. However, Mr Smith believes the satellite technology must have been used to create a figure accurate to within centimetres.

"There were no mistakes — it was very professionally done," he said.

"I can't see how it was done by one person, you'd have to have three or four to do it, and it would take weeks to put in.

"In that case, how has it been kept secret for 20 years?

"You'd think someone would want to skite about it."

Anonymous faxes were sent to the media at the time of the etching

A plaque with an American flag and Olympic rings on it was found at the site, and anonymous faxes were sent to The Advertiser newspaper and the Marree Hotel alerting them to it.

The faxes included American spelling and phrases including referring to "Aboriginal reservations".

However, Mr Smith said this might have been a red herring.

Entrepreneur and explorer Dick Smith.

Some years later Marree Hotel publican Phil Turner and other locals worked for five days to plough the faded outline back into the desert sands.

At the time he told the ABC it was "about restoring the myth and the mystery".

"We did everything we possibly could to ensure we're doing justice to the original creators," he told ABC Radio Adelaide.

"It's about what we, in the far north of SA, can develop and I think now we've got a long-term, sustainable attraction that hopefully will provide a lot of benefits.

"We desperately need tourism and I think everyone in the area recognises that."

In 2017, the SA Environment Department launched an investigation into illegal land-clearing associated with the restoration, which the new Liberal State Government vowed to scrap.

Information might never be revealed

As for what Mr Smith would do with the information?

He has said he is open to keeping it a secret.

"If somebody rang me up and said, 'Dick, I want the $5,000 but on the understanding you won't tell anyone', and then gave me the evidence," he said.

"Tell you what I'll give them the $5,000 and then keep it secret.

"But then I'm going to tell everyone, 'I know who did it, but unfortunately they don't want to be known so you're going to have to do your own work to work it out'."