When the Heroes answer the call of the Horn at the end of the The Great Hunt, Artur Hawkwing makes the following remark to Rand during their pre-battle meet-and-greet:
“It takes more than bravery to bind a man to the Horn.” Artur Hawkwing’s voice was deep and carrying, a voice used to giving commands.... “Only a few are bound to the Wheel, spun out again and again to work the will of the Wheel in the Pattern of the Ages. You could tell him, Lews Therin, could you but remember when you wore flesh.” He was looking at Rand.
Despite not saying it outright, the passage above seems to be strongly suggesting that Rand is also bound to the Horn. I also remember thinking during my first read through the series that of course Rand would be tied to the Horn; the Heroes of the Horn (HotH) are bound the Wheel so that they may be called back in times of great need to fight the Shadow, which (in broad strokes) is basically quite similar to the Dragon's purpose.
Having taken this as just an obvious fact all this time, it only now occurs to me that Rand being a HotH might not make much sense after all. For one thing, it seems superfluous to have him bound to an artifact that only calls back dead people for the purpose of fighting a battle he was specifically reborn for.
A bigger problem with tying Rand to the Horn (which only becomes apparent later in the series) is that it's inconceivable that Lews Therin would have just cooled his heels in Tel'aran'rhiod for 3000 years and put off figuring out how to seal the Bore 'til the last minute. Yes, there are rules prohibiting interference of this sort while the heroes are between lives. But surely if Birgitte can violate those rules basically on a whim, with her only punishment being stern-grunts of disapproval from her boyfriend, then it would be acceptable for LTT to leave some kind of message to his future self, right?
Is there any canonical answer that sorts this out?
I largely suspect the Horn of Valere in general and lore surrounding it were initially intended to play a larger role in the series back when RJ was telling his publishers that the Wheel of Time would be a trilogy, so there may have been plans for Rand and the Horn that were abandoned during the writing process.