Answer:
The answer is a lantern.
Step-by-step explanation:
Old North Church was located in the North End, Boston and it is considered a mission regarding the Episcopal Diocese of Massachusetts. The lanterns were used in the Old North Church to warn Charlestown patriots that were across the Charles River concerning the different British Army's movements.
This method in which the lantern was used was important because it allowed informing the back-up riders that were in Charlestown regarding the British movements. These back-up riders' purpose was to warn Lexington and Concord in the case that Revere and Dawes were arrested.