Ship name prefix: "USS" yes or no? I was thinking of doing "UES" for United Earth Ship.
Fandom until now has generally assumed that the organization doing the fighting for Earth was named something like United Nations Space Navy (an old
Spaceflight Chronology favorite, with "UNSS" prefix on registries), or perhaps United Nations Solar Fleet (as mentioned elsewhere in
Spaceflight Chronology).
However, modern speculation should take into account the concept of there being a "United Earth" rather than a "United Nations", as well as there probably being a coalition of forces on the Earth side instead of just a human-only force. ENT suggests there was very little in the way of warships available to Earth originally, so the ships that fought in the war might have largely been new ones, with the pennants of some new organization painted onto them; prewar United Earth Starfleet types were shown to lack pennant paint altogether, save for the two NX ships.
Number prefix: NCC? NC? NAR? I was thinking I may even go with none at all and just have the number, like a real naval vessel.
Real vessels do tend to have lettering there at times. It's not a USN practice, but many European navies have a D, F or C there in actual paint to denote destroyer, frigate or corvette (although one should remember that those designations won't exactly match the USN designations of the same name). And of course USN uses lettering for bookkeeping even though not in pennant paint - and customarily doubles the letters, so that we have DD, FF and BB, and probably would have CC as well if the USN had believed in cruisers during the Cold War and had not lost the tradition.
Since we never saw more than one prefix for the prewar UESF, we could speculate on there being lots - specific to the ship "mission category", just like those D, F and C are in the real world. NX might be for eXploration ships, so NCC might well be a Cruiser, while NDD and NFF might denote smaller combatants and NBB really big ones.
Of course, UESF may cease to be once the war gets going, possibly but not necessarily replaced by some intermediate organization until the UFP Starfleet comes along.
The current line of novels keeps the UESF but introduces hordes of
Daedalus class ships (there a prewar type that can be easily mass-produced) that get NCC registries. That line of books may not be to everybody's liking, though.
The computer game ST:Legacy gives straight NCC registries to all the various wartime types featured there, apparently including production-standard successors to Archer's
Enterprise...
Timo Saloniemi