The knights lifted the visor of their armor helmet to identify themselves. They used to show their peaceful intentions by raising their right hand, the only one able to hold the sword. This custom occurred whenever they crossed each other during their private journeys as well as during fights.
The meaning of the gesture evolved in the Middle Ages. At the beginning of a fight the opponents raised the visor of their helmet to show their faces. They exchanged “eyes in the eye” as a sign of respect.
Later, salvation became a sign of loyalty between several defenders of the same flag or seigniory. They then raised the right hand by spreading three fingers, which represent the three persons of the Holy Trinity.
Today we do not greet the same way in different countries, the hand is not always positioned in the same way.