Jess Nevins of io9 has pictures of the tombstone marking the grave of Rev. Ichabod Wiswall (1637-1700) in Duxbury, Massachusetts. Though largely forgotten today, Wiswall was a prominent political figure in 17th Century Massachusetts. It is unclear why his grave bears the image of cosmic entity Cthulhu:
Duxbury does not feature in any of Lovecraft's fiction; "Arkham" is based on Salem, "Innsmouth" is based on a combination of Ipswich and Gloucester, and "Dunwich" is based on Athol. But Duxbury was no stranger to sea serpents, even in Wiswall's day. The English writer John Josselyn's An Account of Two Voyages to New-England (1674) described the 1639 sighting of a sea serpent off Cape Anne, north of Duxbury, which sparked a rash of sea-serpent sightings along the Massachusetts coast, including Duxbury. And in 1857 Henry Thoreau wrote in his journal that Daniel Webster had seen a sea-serpent off the coast of Duxbury.
So it makes a kind of sense for a Lovecraftian cephalopod to appear on the Reverend Wiswall's gravestone. The only question remaining is, is Wiswall dead in his grave, or does he merely wait there, dreaming?
In the comments, propose your own explanation for the mark of Cthulhu on this gravestone.