If you want to know the true meaning behind South Carolinas' Cresent, you'll get different stories, depending on who you ask.
The first option you have is that it is a gorget, which was the crescent worn on the caps of the South Carolina revolutionary soldiers. This version is actually what most people believe.
The other choice seems to make a lot of sense too, though. In European history, the crescent was a symbol that represented towns founded on the banks of a river loop. Charleston, or Charlestowne, was the founding city of what became South Carolina, and was established on a "loop" of the Ashley River. So the image on the state flag could represent the founding city of Charlestowne.