In England, giving someone the 'v' sign (as Clive says, with the back of the hand towards the watcher) means much the same as showing your middle finger in the US - that is, expressing "f*** off!" or "f*** you!". It's not sexual. If you mean it to be less agressive, it's often accompanied by blowing a raspberry.
The common understanding of the origin of the 'v' is that it emerged during the wars with the French in the 15th century. The English army had archers using long bows, which caused devastation to the French troops. As an expression of contempt, the English are said to have waved the two fingers you would use to draw back the string of the bow at the French. I have no idea whether this is historically accurate.
If you turn the 'v' around so your palm faces the watcher, it means 'peace' or 'victory'.