"King," croaked the raven. The bird flapped across the air to land on Mormont's shoulder. "King," it said again, strutting back and forth.
"He likes that word," Jon said, smiling.
"An easy word to say. An easy word to like."
"King," the bird said again.
"I think he means for you to have a crown, my lord."
"The realm has three kings already, and that's two too many for my liking." Mormont stroked the raven under the beak with his finger, but all the while his eyes never left Jon Snow.
: This could be the random spoutings of a raven. Or it could be a subtle clue that Jon, as the only surviving son of Rhaegar, would be the king of Westeros if the Targaryens still reigned.
As one last tidbit of evidence, it can be said that if Jon is the son of Rhaegar and Lyanna, it fits with the series name 'A Song of Ice and Fire.' Jon seems to be shaping as the main character, and it woudl fit the series title if his parents were Rhaegar (fire) and Lyanna (ice).