In [ACOS: 14, White Plumes, 280] Mat acquires a signet ring, by pure "luck." The ring is gold with a dark oval carved stone, and is in the "long style"; the stone is as long as the joint of Mat's finger [ACOS: 14, White Plumes, 279]. Here is a description of the carving: "Inside a border of large crescents, a running fox seemed to have startled two birds into flight." [ACOS: 16, A Touch on the Cheek, 300] We get a more specific description in WH: "...a running fox and two ravens in flight, all surrounded by crescent moons..." [WH: 17, Pink Ribbons, 371].
The fact that Mat was "forced" into buying the ring by his luck made us suspect that the ring would play some important role in his future. Most people thought that this role would have something to do with the Seanchan (and the DotNM) even before we knew for sure that the birds were ravens and the crescents were moons. (Ravens are an Imperial sigil to the Seanchan [WH: 18, An Offer, 387].) Jason Kraftcheck observes, "Ravens for Seanchan, moons for The Daughter of the Nine Moons, and Tylin later refers to Mat as a fox [WH: 31, What the Aelfinn Said, 582]."
When Tuon and Mat meet for the first time in WH, she inspects him closely and seems to pay special attention to his ring [WH: 17, Pink Ribbons, 371]. It is immediately after examining the signet that Tuon offers to buy Mat from Tylin, and later she demands to know why he isn't wearing it [COT: 3, A Fan of Colors, 140]. Coincidence?
We discover in KoD that Tuon's damane, Lidya Foretold the following: "Beware the fox that makes the ravens fly, for he will marry you and carry you away. Beware the man who remembers Hawkwing's face, for he will marry you and set you free. Beware the man of the red hand, for him you will marry and none other." [KOD 36: Under an Oak] Tuon recognized the ring as marking her future husband, which explains why she was so willing to be kidnapped and never tried to escape Mat's custody.