Heralds came about due to the lack of an effective means of information transfer, and were precursors to the communication system of modern times.
During the ItalianRenaissance, should Ezio Auditore commit a crime, the heralds would begin warning the people about the presence of the Assassin. To keep himself hidden, Ezio would often bribe them with 500 florins, and encourage them to speak of other matters. Similarly, in Constantinople, Ezio would bribe heralds with 100 Akçe.
When viewed through Eagle Vision, heralds were marked with blue if they were announcing normal events. If they spoke of the Assassins (mostly lies and slander), they were seen glowing red, as any other enemy. They sometimes also glowed yellow.
In Assassin's Creed, certain people may be found speaking publicly, attempting to convince citizens to join the Crusaders or Saracens. These men functioned much like heralds, although they were not referred to as such, and were purely aesthetic.
In Assassin's Creed II, heralds would appear on the map as long as Ezio's notoriety was not at 0%. In Assassin's Creed: Brotherhood, notoriety must have been greater than 50%, and in Revelations, they appeared around 25% Templar awareness. It should be noted that, in Assassin's Creed II, in Venice they appeared at 50% notoriety.
In both Brotherhood and Revelations, it was possible to steal back the money that Ezio used to bribe heralds, though they would initiate a fistfight should Ezio remain in the area afterwards. The Brotherhoodachievement "Easy Come, Easy Go" could be earned by doing so.
In this achievement, a herald is referred to as an "orator."
The heralds of Rome in Assassin's Creed: Brotherhood warned about swine flu and syphilis, while in Assassin's Creed II, they warned citizens about plague.