"VNVM" is on ALL Standing Liberty quarters. It's part of the motto E PLURIBUS UNUM. Please see the Related Question for values.
To explain the apparenly strange spelling, in the early 20th century it was popular for artists to use the Roman alphabet instead of the English alphabet. The Roman alphabet only had 24 characters; the symbol "V" was a consonant, a vowel, and even a number.
The famous Peace dollars from the same era also used Roman lettering, so they read IN GOD WE TRVST instead of "TRUST". It's not a mistake, just artistic usage.
The motto of Viceroyalty of New Granada is 'Vtraque Vnvm'.
Denis Godefroy has written: 'Corpus iuris civilis romani' -- subject(s): Roman law, History 'Avctores latinae lingvae in vnvm redacti corpvs' -- subject(s): Grammar, Latin language