The rocks were spotted by a helicopter pilot last month, prompting fears that someone, or more than one person, could be missing.
Police now believe it was likely to be a genuine distress signal left by a man and woman who became stranded in 2013.
They say they were contacted by the brother of the man, who read about the case on the BBC.
"The brother actually saw an article on the BBC," Senior Sgt Dave Rudd of Western Australia Police.
The man, called John, said his brother - identified only as Robert - and a female companion were aboard a yacht that became stranded at Swift Bay, about 500km (300 miles) from the city of Broome in 2013.
The pair boarded an escape raft which at some point "was attacked by a couple of crocodiles" but made it to shore safely and built the SOS signal.
Senior Sgt Rudd said they survived on rations, found some fresh water and were eventually rescued by another passing yacht.
Police said they have not been able to speak directly with Robert because he is on a boat in the Mediterranean Sea.
But they said they had seen photographs showing the distress signal taken at the time the pair ran into trouble.
"We can see from the photo that it's the same location and the same SOS," Senior Sgt Rudd said.
"We're very confident it's legitimate and it's the real deal but until we speak with him there's still a few unanswered questions."
Police say they may have found out who left an SOS signal made of rocks in a remote part of Western Australia.