Another website find while looking for something else. Over at voicesunderberlin.com, I ran across this seal for Army SIGINT with an explanation of the symbolism behind it.
Explanation of the Symbolism
The American eagle proper displayed on a dark blue field. The dark blue background signifies vigilance and loyalty. The eagle’s head is shown affronté with its head turned to dexter, the direction of honor.
In its dexter talon the eagle is holding a lightning sword by a golden hilt. The lightning sword is the symbol of military SIGINT. It alludes to the offensive and defensive requirements of the mission, as well as to the element of physical danger potentially inherent in its completion. The color gold signifies successful accomplishment of the mission. In his sinister talon the eagle grasps a golden double-warded key, the symbol of cryptography.
In his beak, the eagle is holding a scroll, inscribed with the Latin motto: Semper Vigilis (Always Vigilant). The escutcheon on the breast of the eagle displays a talon seizing two lightning bolts, symbolizing the communications intercept mission of Army SIGINT. This was an element in the original insignia of the United States Army Security Agency (1945-1976).
The eagle’s position under a rose (sub rosa) symbolizes secrecy, a requirement perforce for the continued success of the unit’s mission. The red of the rose symbolizes hardiness and valour. The Latin motto Ex Æthere Gnaritas(Knowledge from the Ether) above the rose further elucidates the symbolism of the escutcheon.
Beneath the eagle is a third, encrypted motto, amplifying the symbolism of the double-warded key, explaining why Army SIGINT units have traditionally been so successful.