The arms were: Azure a sword per pale argent hilted or between a crown in chief and two fleurs-de-lys of the last. The symbolism of the arms is fairly obvious.
She testified at her trial that she never used those arms personally, only displaying her famous banner (white, with an image of God holding the world between two angels, and the words Jhesus Maria). The arms were also granted to her family, and it must have taken place in 1429. The family was also authorized to adopt the name of Du Lys.
The text of the grant of nobility (Dec 1429) survives. It was made in favor of her parents, her three brothers Jacquemin, Jean and Pierre, and their descendants male and female, in perpetuity. Thus, in her family, nobility was transmitted by females. It was confirmed in October 1550, on petition of Robert Le Fournier, baron de Tournebeu, and his nephew Lucas du Chemin, seigneur du Féron, both descended from a daughter of Pierre du Lys.
The family seemed to have arms prior to these events, namely: Azure a bow or in fess, thereon three arrows crossed …, on a chief argent a lion passant gules.
Of her three brothers, two had issue: the descendants of Jean adopted the name of Du Lys and used the arms. Pierre, who became a knight, had two sons: Jean, knight, who left only a daughter, and Jean the younger, who was briefly Échevin of Arras in the 1480’s. He returned to France and kept the name of Du Lys, but resumed the arms of Arc. His great-grandsons Charles and Luc du Lys, seigneur de Reinemoulin, petitioned for the right to quarter du Lys and d’Arc, which was granted by Letters Patent of November 25, 1612.