Although it was made by Morgan le Fay, I find no indication that this shield was magical in itself.
The field was goldish, with a king and a queen therein painted, and a knight standing above them, [one foot] upon the king's head, and the other upon the queen's.
Morgan made Tristram (Tristan) carry this shield in the tournament at the Castle of the Hard Rock. The device signified Arthur, Guenevere, and Lancelot, although Morgan would not tell Tristram who the painted knight was.