The spade symbolizes wisdom, acceptance and labor. It is also represents earth in regard to the four elements and is a leaf from the cosmic tree representing life. When combined with clubs, the spade represents fall, winter and the power of the dark. In regards to the tarot, spades represents death, action, air and intelligence.
During World War II, members of the 506th Parachute Infantry Regiment and the 101st American Airborne Division both wore the spade as a symbol of good luck. The spade marking also helped to identify these regiments within the airborne division with dashes or dots at different positions helping to identify the battalions within the regiments.
During the Vietnam War, soldiers wore the spade as a psychological weapon against the Viet Cong soldiers as a symbol of death and ill fortune. The idea was to scare away the soldiers without having to engage in a fight. Soldiers were known to leave an ace of spades card on the body of a fallen Viet Cong soldier and to litter battle grounds with the cards to scare the enemy. The practice occurred so frequently that the United States Playing Card Company manufactured only ace of spade cards to be sent overseas.