There's an excellent depiction of a younger Maekar in THE HEDGE KNIGHT graphic novel. As king, Maekar would look much the same, only older. A certain weariness about him, but strength as well. Armored, with a spiked mace in his hand (blood on one of the spikes). His crown is black iron and red gold, sharply pointed. His surcoat shows his personal arms; the Targaryen three-headed dragon, four times (two above, two below).