The Shugnahoth is the ensignia, and symbol of the Empire. It is as early as the Empire itself, and was said to have been carved into the flesh of the Emperor as a divine message that he would unite the Prime Material Plane under this banner.
The Shugnahoth is as early as the Empire’s founding. N’nosk, the Emperor, declared that the entirety of the Prime Material Plane would be united under the symbol carved into his flesh. That symbol was the Shugnahoth.