The Galactic Empire: An Empire Reborn
Imperial Officers' Manual
Major Revision: 2.0 – 2008.10.31
An adaptation of the pre–Endor document and policies.
RIP
... A Staff Sergeant's Rank Insignia...

The rank of Staff Sergeant (SSG) is used to reward Sergeants who have performed significantly long and valuable service to the well-being of their companies or within the Imperial Army as a whole, but do not wish to become a commissioned officer. This rank can also be used to recognize an officer who would normally be a commissioned officer, but lacks an available opening in an appropriate unit.

These officers are very familiar with how the Army operates and have proven themselves both loyal and capable in battle. As such, they are also charged with mentoring and guiding junior members and assisting their commanders when needed.