The phrase 'Two if by SEA' is a reference to the poem 'Paul Revere's Ride' by Henry Wadsworth Longfellow. The poem tells the story of Paul Revere's midnight ride to warn the colonists of the British invasion during the American Revolution. The phrase 'two if by SEA' refers to a signal that Revere was to watch for, two lanterns in the Old North Church tower, which would indicate that the British were coming by SEA.