From Halopedia, the Halo wiki
SolCore is an organisation or establishment associated with humanity, and presumably the Sol system. It is unclear what precisely SolCore consists of, though its emblem can be found printed on the CQS48 Bulldog shotgun.
During the production of Halo: Combat Evolved, SolCore was the original name for the central human government in the Halo universe before being changed to the Unified Earth Government and its United Nations Space Command. By the time SolCore encountered the Covenant it had colonized seven worlds and discovered four "lost colonies" of humans. The UNSC Pillar of Autumn's original hull classification symbol, SCS, presumably stood for SolCore Ship.
The SolCore concept was revived and reintroduced into canon as a graphic applied to the CQS48 Bulldog shotgun in Halo Infinite.
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