Jon is a bastard who joined the Night's Watch so he doesn't have any coat of arms nor the right to one.
he is killed and resurrected, he becomes King in the North. Just as any king, he would need a coat of arms.
Therefore, I expect he now (Season 7) would or should have a coat of arms.
In the image below we can see a double Stark direwolf. (but no colors, nor any indication that it will always be 2 wolves, ...)
Does he use the same one as the Stark's? Did he slightly modify (play with colors, or mirror it) it like some other (mostly regulated) bastards did? Or did he create a new one based on the Stark one?