For the record, when the Raven
first appeared in "The Raven," the clearly-visible dedication plate gave its name as S.S. Raven
Only in "Dark Frontier" was the Raven
referred to as the "U.S.S. Raven
," in dialogue, by Magnus Hansen in the ship's log.
Personally, I'm inclined to ignore the dialogue and accept that it's just the S.S. Raven
, because it's obviously being crewed by civilians.
The notion that it was a decommissioned Starfleet ship that was sold to civilians makes sense. TNG established a precedent for that when the Oberth
-class S.S. Vico
from "Hero Worship" was depicted as a civilian ship.