From A to Z;Primary
V is for victory not just in English but in many Western European languages so v was a vivid symbol of Allied defiance during the Second World War. As well as Churchill's two-fingered indication of Allied intentions, the BBC used the opening notes of Beethoven's Fifth as a v-sign in broadcasts (v in Morse Code is dot-dot-dot-dash).
To an Ancient Roman, however, v was for "wictory". V and u were the same letter in Latin, pronounced "w" before a vowel (as today in the words linguistics and suave). Fortunately, fifth-century English scribes decided to put two vs together for the "w" sound, so v was given a valuable voice as a consonant. Despite this, u and v were still used interchangeably in texts until the 18th century, and spellings like haue and vpon were common.
I can only think of two spelling rules relating to v. The first is that it cannot finish a word. Thus have, give, love and so on, need a final silent e to finish them off. Unfortunately, the rule collapses in the face of slang and abbreviations: spiv, lav, Rev.
The second rule is that final f changes to v when adding an ending changes the pronunciation. You see (and hear) this when nouns turn into verbs (belief - believe, shelf - shelve) or singulars into plurals (self - selves, wife - wives). But where pronunciation doesn't change, neither does spelling (as in chiefs, roofing, selfish). A couple of words (hoofshooves, dwarfsdwarves) have optional spellings depending on how you choose to say them.