The modern salute originated when knights greeted each other to show friendly intentions by raising their visors to show their faces.
Raising one’s visor was common practice and considered basic courtesy in tournaments.
Bonus fact 1: Originally knighthood was not a hereditary title. Any free person – that is to say anyone who was not a serf – that had enough money to buy a horse, armor, and essential training could become a knight. They swore allegiance to a wealthy nobleman and served as his bodyguard and professional soldier.
In those days sons of noblemen that were not firstborn were not entitled to the inheritance. Hence most of them became kights or joined the clergy. Both careers required some capital to kick-off, which was usually given by their father. However, as said, anyone with enough capital could become a knight.
It was only in the late 12th century, with the decline of the military importance of the knights and, in accordance, demand for their services, that the title became hereditary, synonymous with the aristocracy, and hence a significant symbol of status.
Bonus fact 2: Following the Crusades, a new kind of knight emerged – the Knights-Monks. Christian religious military orders were established in the Hollyland and Europe whose members swore allegiance to God and not to any nobleman. Their high discipline made them an effective army. As monks, they didn’t, or at least we’re not supposed to have kids and hence, by definition, it was not a hereditary title.
Despite their oaths of nunhood and modesty, these orders accumulated great political and economic power, and also amassed a huge fortune, which made the secular kings of Europe envious of them. The most famous religious knights’ orders from that period were the Knights Templar Order, the Templars, the Hospitallers, and the Teutonic Order.