By Grabthar's Hammer-
Oh no, wait...
I honestly never put any thought into a ship's motto. The one "ship" to which I was ever assigned never had a motto, so it never occurred to me.
I think if I had to come up with one now, it would probably be for the U.S.S. Tannhauser Gate.
Semper Fi, do or die, MACO leads the way! Oorah!
An obvious corruption of a Marine Corps cadence (replacing "Raise em high at 8th and I.") and the Rangers motto (Rangers lead the way), since MACO is an incorporated Earth military organisation which likely saw the unification of the Marines and the Army as Starfleet is a likely unification of the Navy and the Air Force. (It's my little imaginary world, here, just roll with it. That and I was reaching, a bit.)
Why a MACO motto? The Tannhauser Gate is captained by the character whose biography involves him being pulled from Star Fleet Academy and attending the MACO equivalent (Not sure if I mentioned a location; if I did it was likely Quantico or Annapolis) before being returned to SFA to complete his Starfleet training. But as his bio says, "Once a MACO, always a MACO." So he hand picks his crew from MACO graduates and cross-trainees.
Maybe that wouldn't work, but Hollywood's gotten away with worse. :p