The meaning of this spiral is still unknown, all that is known about it is that all known gyre souls have it. Faolan thinks this design is part of a bigger destiny or greater harmony. It could also mean he is the chosen one or maybe a cursed one. We may never know. But the Spiral Mark is something that no one can begin to explain, but it could mean that Faolan might be or has something special about him that we cannot explain even if some of us sense it.
Also, certain things (mainly in Watch Wolf) seem "hauntingly familiar". For example, when Faolan receives his Watch necklace, it seems "hauntingly familiar". He would also say Old Wolf words, so far unnoticed to him.
Faolan was born with an unknown mark on his left paw, which is also splayed, making him a malcadh. As he is exploring the northern part of the Beyond, coming back from the Outermost, searching for his adoptive mother, Thunderheart (who, unknown to him at the time, is dead), he discovers a cave called the Cave Before Time. He starts exploring the cave, and looks at the markings on the walls of the cave that form pictures and he keeps coming across the same mark on his paw, the spiral mark. Later, Faolan shows the masked owl Gwynneth his paw, and when he leaves, Gwynneth somehow makes a replica of the mark.
In Shadow Wolf, when Faolan caused the byrrgis to collapse, he is to receive a punishment called the "Gnaw Bite". And to make it more humiliating, Heep is assigned to administer it, but he is too scared of the spiral print in the mud to do it.
Faolan is then sent to the Carreg Gaer to visit Duncan MacDuncan. There is a fire in the cave. Duncan begins to wonder if Faolan has the firesight, a rare ability to see through the flames. The chieftain wonders if the young gnaw wolf sees the cold before the summer moons, if the Long Cold would return; but all Faolan sees in the flames is his spiral mark.
In Watch Wolf, when Faolan and Banja begin to fight, Finbar the Fengo says to do Paw Right but Banja is too scared to touch Faolan's malformed paw. She touches it, finally, only to turn away and stumble back, with a shocked expression on her face.
Later in the second-to-last chapter, the Sark and Gwynneth take Faolan to see his first Milk Giver, Morag, who is blind. When they both realize they are mother and son, Faolan lifts his splayed paw and Morag licks the spiral mark. Faolan likes how this felt.
During the Great Mending, Faolan's splayed paw is restored, and now as he walks, he leaves a spiral mark on his pawprint in the snow. The Sark wonders to herself, is Faolan a Gyre Soul? Faolan soon figures Gyre Souls are souls who have lived in the past. His past Gyre Souls are; the first Fengo, Fionula, the snowy owl, and Eo, the grizzly.
Also, when Heep is thinking about Faolan, he supposes that his splayed paw and odd spiraling mark had been mended, as he got his tail back. Later, Abban exclaims that he sees a swirling star in the dirt, which, in fact is a print of Faolan's spiraling mark.