USS Relativity plaque

A 29th century Federation timeship dedication plaque with the NCV prefix

NCV was a three-letter prefix for Federation timeship registry numbers in the 29th century, similar to the NCC prefix commonly found in Starfleet in previous centuries.

One starship known to carry the NCV prefix was the Wells-class USS Relativity (NCV-474439-G). (VOY: "Relativity")

The USS Relativity appeared to have had at least seven previous vessels bearing its name, it was probable that those ships also had a NCV prefix for their registry numbers, based on the Enterprise precedence.
A graphic created for Star Trek Beyond but thankfully not seen in the final movie included several ships with the registry docked at the 23rd century alternate reality Starbase Yorktown. These included NCV-1248, NCV-1539, and NCV-1690.