Not original source.
That image taken from here:
https://newengland.com/today/travel/new-england/best-new-england-revolutionary-war-sites-events/
In the days before April 18, Revere had instructed Robert Newman, the sexton of the North Church, to send a signal by lantern to alert colonists in Charlestown as to the movements of the troops when the information became known. In what is well known today by the phrase "one if by land, two if by sea", one lantern in the steeple would signal the army's choice of the land route while two lanterns would signal the route "by water" across the Charles River (the movements would ultimately take the water route, and therefore two lanterns were placed in the steeple).[44] Revere first gave instructions to send the signal to Charlestown. He then crossed the Charles River by rowboat, slipping past the British warship HMS Somerset at anchor. Crossings were banned at that hour, but Revere safely landed in Charlestown and rode to Lexington, avoiding a British patrol and later warning almost every house along the route. The Charlestown colonists dispatched additional riders to the north.[43][45]
https://en.wikipedia.org/wiki/Paul_Revere
Main article: Paul Revere's Ride
In 1861, over 40 years after Revere's death, Henry Wadsworth Longfellow made the midnight ride the subject of his poem "Paul Revere's Ride" which opens:
Listen, my children, and you shall hear
Of the midnight ride of Paul Revere,
On the eighteenth of April, in Seventy-Five;
Hardly a man is now alive
Who remembers that famous day and year