The Valyrian Steel Oathkeeper is pretty accurate and even uses red Damascus steel to make it look closer to the original from the novels.
However, for some reason it appears to use a depiction of Dunk's Coat of Arms, a green shooting star above an elm tree proper on sunset:
As far as I know Oathkeeper was made for Jaime Lannister:
Tyrion put down Joffrey's sword and took up the other. If not twins, the two were at least close cousins. This one was thicker and heavier, a half-inch wider and three inches longer, but they shared the same fine clean lines and the same distinctive color, the ripples of blood and night. Three fullers, deeply incised, ran down the second blade from hilt to point; the king's sword had only two. Joff's hilt was a good deal more ornate, the arms of its crossguard done as lions' paws with ruby claws unsheathed, but both swords had grips of finely tooled red leather and gold lions' heads for pommels.
"Magnificent." Even in hands as unskilled as Tyrion's, the blade felt alive. "I have never felt better balance."
"It is meant for my son."
A Storm of Swords, Tyrion IV
Who then gifted it to Brienne of Tarth:
Brienne approached as if the bundle was like to bite her, reached out a huge freckled hand, and flipped back a fold of cloth. Rubies glimmered in the light. She picked the treasure up gingerly, curled her fingers around the leather grip, and slowly slid the sword free of its scabbard. Blood and black the ripples shone. A finger of reflected light ran red along the edge. "Is this Valyrian steel? I have never seen such colors."
"Nor I. There was a time that I would have given my right hand to wield a sword like that. Now it appears I have, so the blade is wasted on me. Take it." Before she could think to refuse, he went on. "A sword so fine must bear a name. It would please me if you would call this one Oathkeeper. One more thing. The blade comes with a price."
A Storm of Swords, Jaime IX
So why does the plaque use Dunk's coat of arms?