From Halopedia, the Halo wiki
The Crew emblem is a symbol that represents a UNSC ship.
Ship emblems are usually worn by command personnel, most notably the captain of the ship. Some of these emblems usually contain the ship's name and hull classification symbol as well as images or other information related to the ship.
UNSC In Amber Clad
UNSC Pillar of Autumn
UNSC Spirit of Fire