The 'V' sign, made by holding up the index and middle fingers, initially was used to signal victory by Allied nations during World War II. Anti-war activists later adopted it as a symbol of peace, and today the gesture is known as "the peace sign."
… but flip it around, and in some countries it's like giving someone the finger
In certain Commonwealth countries, including the United Kingdom, Ireland, Australia, New Zealand, and South Africa, an outward-facing V sign is an obscene gesture equivalent to giving someone the middle finger.
The gesture is often performed by flicking the V up from the wrist or elbow.
You might throw up the devil's horns at a rock show, but in some countries you're telling someone their wife is cheating on them
Heavy metal fans are familiar with the so-called "sign of the horns" or "devil horns," made by extending the index finger and pinky.
But in many European and South American countries, including Italy, Spain, Greece, Brazil, Argentina, and Colombia, the gesture has a more obscene meaning.
There, it's used to mock cuckolds — husbands whose wives are unfaithful. The connection is obvious to people from those countries: the word for "cuckold" in Italian, Spanish, and Greek is the same word for "horned."
This looks like an 'OK' sign, but not in Brazil
Making a circle with your thumb and your index finger is how to signal "OK" in the US.
But make the same gesture in Brazil, and you're giving the equivalent to the middle finger — the gesture has "insulting and scatological connotations," as the New York Times put it. Richard Nixon once raised some eyebrows in the 1950s when he made the gesture in Brazil as he stepped off a plane.
And definitely don't give a thumbs up in the Middle East
The thumbs-up gesture is a sign of approval in most countries.
However, in several countries in West Africa and the Middle East, including Iran, Iraq, and Afghanistan, the gesture has the connotation of "up yours!" It's used the same way the middle finger is in the US.