A mystery SOS sign made of rocks has prompted fears that a person or persons could be missing.
The distress signal was spotted by a helicopter pilot flying over the remote region of Kimberley in Western Australia.
A police ground search soon followed but failed to find any indication of recent human activity.
However police did say they discovered the remains of a campsite at the scene.
Authorities are now appealing to the public for information.
Western Australia Police said on Facebook: "Kalumburu Police wish to speak to anyone who may have been in the Swift Bay (Kimberley) area over the past few months who can assist them with locating the person(s) who made an SOS sign.
"Police are trying to establish if there are any missing persons in the area who require assistance."
Senior Sgt Peter Reeves told the Australian Broadcasting Corp it is difficult not know for how long the message has been left there.
He said: "There are indications that there may have been someone camped there at one point in time, but it is just not clear how long ago that was.”
In 2015 a couple who were stranded on a desert island for a week were rescued after a plane spotted their 20ft SOS message written in the sand.
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