Regarding Paul Revere's signals
http://www.paul-revere-heritage.com/one-if-by-land-two-if-by-sea.html
"Few days before the historic ride, Revere was preparing his mission and arranged with three fellow patriots to set up a light signal in case if British troops started their advance to Concord. To give even more information, it was agreed that one lantern meant that the troops chose the longer land route and two lanterns meant the shorter route by water, leaving less time for patriots to react."
"Despite its historical significance, the “One if by Land Two if by Sea” signal was just a backup plan. It was meant to warn patriots in Chalrestown, a borough across the river from Boston in case if the messenger himself could not make it there from Boston to start his ride. With so many British troops present in Boston at that time P.R. could easily be arrested by patrols. But at the end he was able to safely leave Boston by boat and ride himself so the signal was in fact redundant. With this a popular myth was created that the lanterns were intended for Revere himself who was waiting for the signal across the river."
Latern's were a backup plan