According to this Q&A with his editor Anne Groell, GRRM foreshadows all the time as part of his "three-fold revelation strategy":
Q: Anne, although you're the envy of many a GRRM fan, do you ever wish you didn't have to edit the books so that you could be surprised by them all at once along with the rest of us?
A: No. As above, he doesn’t tell me a lot. He feels I am most effective at my job if I am surprised along with everyone else. And it is easier to tell when he’s overplaying a hand and revealing things too early if you don’t actually know going in what will happen. That said, now that I’ve realized his three-fold revelation strategy, I see it in play almost every time. The first, subtle hint for the really astute readers, followed later by the more blatant hint for the less attentive, followed by just spelling it out for everyone else. It’s a brilliant strategy, and highly effective.