It could also be that Starfleet surplus ships retain Starfleet colors - perhaps that's what's going on with the Raven
? The Hansens might have purchased an old Starfleet vessel whose log computers still insist on inserting the USS thing there, but they'd still be a civilian outfit through and through, under no obligation to report to Starfleet or return the hardware at mission conclusion or anything like that.
Hmm. Do companies, corporations or businesses still exist in the 24th century? Do they even exist in the 23rd?
We at least see individual entrepreneurs interested in profit in the 23rd, and hear of some in the 24th (the Vulcan who upped the price of an object when he learned Janeway, the buyer, was from Starfleet) even if we discount criminals who might be dealing outside the UFP (say, the explicitly profit-interested "Starship Mine" folks). But those never amount to an actual organization
with employers and employees.
We don't see UFP corporate logos up close at any point (although in-jokes on Okudagrams about the Yoyodyne Corporation and the like might be legible in some shots). And we never hear the name of a corporation or a company mentioned in dialogue. Or do we?