I always thought the V sign was a kind of symbolic "F* you" with two fingers shoved up where they are not wanted then forced apart for emphasis and extra pain.
It is the first letter of Victory, and Beethoven Fifth Symphony (da da da daaa) was played by the BBC before broadcasts to occupied France.
It is sometimes explained as the two fingers which draw back a bow with the arrow between them (*Bags"? ) as used by English archers as they trounced the French at Agincourt, or the horns of a cuckold - but the cuckold sign was with the index finger and pinkie, so I don't believe that.