Borgia messenger

Borgia Messengers, also known as Borgia Couriers, appear in the game Assassin's Creed II and in the short film Assassin's Creed: Lineage. Upon spotting Ezio, the messengers take flight, performing many free-run actions and acrobatic stunts, such as climbing walls and swinging from posts. If Ezio manages to catch up to one, he can tackle him or simply throw a Throwing Knife at him for a considerable amount of florins, with about 1,500 florins per messenger. However, if Ezio kills one, his notoriety will automatically increase by 50%; though he can still get the florins if he loots the body. If caught, the messenger begs for his life. After being attacked or left alone a few moments, the messenger will resume his free-running.

Presumably, the messengers carry important information or funds for Rodrigo Borgia, as they are called Borgia Messengers. They may also be carrying payment to or from some official or ally, explaining the 1,500 florins in their possession.

Interestingly, Archers begin chasing the messenger as well if he climbs onto a rooftop in his flight. This is rather ironic, as messengers often call to the guards for help during the chase. It has also been shown that you can trip Borgia messengers, or throw them off buildings so that they fall to their death without being penalized for it.

If you intercept one of them, you get the Achievement/Trophy "Mailman" (10G)

Unlike Pickpockets, who have a red icon, Borgia Messengers are invisible on your map; although you can often find them at city entrances, and they are pointed out by a silver chevron. For some reason, the messengers often move rather slowly when on flat ground directly after a free-run up the side of a building. They can easily be taken down by a well-aimed throwing knife during these periods.

Trivia

 * Perotto Calderon was a Borgia Messenger but secretly an Assassin.