From the source:
The Shield:
The colors dark blue and gold represent the United States Navy. The two chevronels in base recall Corporal Dunham’s rank. The scarlet pale represents the Marine Corps and refers to the trouser stripe worn by Non Commissioned Officers. The Marine Corps Non Commissioned Officers sword on the stripe is point down, signifying Cpl Dunham’s sacrifice of his life to protect his troops. The helmet of antiquity recalls the service traditions of brotherhood which hold true today and recalls the incident of enemy attack on Cpl Dunham’s squad during which he used his helmet to contain a grenade and covered it with his body to protect his squad at the cost of his own life. The purple detail on the helmet refers to the Purple Heart Medal awarded Cpl Dunham. The distinctive shield shape is that used on the state arms of New York, Cpl Dunham’s home state. The gold mullet in dexter chief signifies the loss of Cpl Dunham to his service and his family. The gold border denotes the unity and cohesion of Marine Corps service members which characterize the force and clearly influenced Cpl Dunham’s action in defense of his troops.
The Crest:
The decorations awarded to Corporal Dunham are represented along with the eagle, globe and anchor insignia of the United States Marine Corps; the inverted mullet symbolizes the Medal of Honor, the nation’s highest decoration for valor awarded to Cpl Dunham for his sacrifice in protecting his squad, and the Combat Action Ribbon, awarded to him along with the Purple Heart Medal, which is referenced on the antique helmet appearing on the shield.
The scroll under the shield reads:
SEMPER FIDELIS SEMPER FORTIS