I've got a fair amount of experience with cats, but I've never seen this posture in another cat.
My one cat holds his tail forward, arching over his back, with the tip just a few inches behind the back of his head.
His tail seems to have the normal range of motion, but he always holds it in the same position when walking or standing.
He's a neutered male, if that is relevant.
Is there a physical reason behind this, or is it some behavioral indicator, or related to his social status relative to our other cats?