I.G.S. and I.G.V. appear to be available on the new Andorian ships. I am unsure if there are other registries -- whether they're name, number, or both, and for one, or all Andorian ships. --MatthewM 23:33, 21 February 2013 (UTC)
So I saw a registry of U.X.X.X. I don't know where it came from.
Lukari ships default to "L.S.S.", presumably for Lukari Star Ship