Are they separated from the Orbit Guard?
The IGBV aren’t part of the Watch Constabulary or other policing organizations; they’re exactly what the name implies, the border guard. They’re the ones who stand on the mostly-metaphorical wall[1] and declare “Civilization, this side. Everything else… over there,” with the necessary means to back it up.
They also run the inplacement/outplacement processes at border crossings, sorting folks to the appropriate sides of the wall like immigration-focused Maxwell’s Daemons.
The Empire doesn’t have a lot of land borders these days, but not a lot isn’t the same thing as none. ↩︎