Red Comet

The Red Comet, also called the Red Messenger or Red Sword, is an astronomical phenomenon. It appeared in the skies over both Westeros and Essos shortly after the outbreak of the War of the Four Kings and the hatching of the dragons of Daenerys Targaryen.

Season 2
The Red Comet can be seen in the skies over most of the two continents. Its significance is discussed by the people of Winterfell, who seem divided on it being an omen of King Robb Stark's victory or if its red color indicates a triumph for the forces of House Lannister. However, the wildling woman Osha is convinced that the comet means that dragons are once again alive somewhere in the world.