When activated, the player's team mates that died in his general area will respawn on him. This option is outstandingly good when it comes of need of backup behind enemy lines, making flag capture easier. However, its "reload" time start as soon as the player using it dies or enters on a vehicle and is painfully slow, making it also an option risky to use, losing a gold opportunity which could make a difference in the game.
Request Reinforcements highlighted in the Combat Expertise training options
Symbol of Request Reinforcements, as seen on the Weapons inventory