I believe theyre referring to the usual two-finger-fuck-you. As in v for victory.
If you take that same sign and press it to your lips you get a gesture recognised as "eating pussy" when accompanied by some tongue action through the V of your fingers.
Ah, I see. We don't tend to put it to the mouth. It's more "fuck you". Apparently comes from demonstrating to the French that you still have your bow-drawing fingers and intend to use them. British archers captured by the french would have their first two fingers removed to prevent them launching arrows.
A commonly repeated legend claims that the two-fingered salute or V sign derives from a gesture made by longbowmen fighting in the English army at the Battle of Agincourt (1415) during the Hundred Years' War, but no written historical primary sources support this contention.
The human race is often thought of as communicating primarily on a vocal basis. however, they also possess an extremely complex and sophisticated language based on gestures. For example, the simple gesture of raising the index and middle finger with the palm inwards can convey the complete sentence: "up yours Frenchie, I still have all my fingers"