Similar indeed, but Plymouth's Mayflower logo seems to show the back of the ship, and headed a different direction.
If this thing is a letter opener, it looks like the sheath is stuck on... unless its the chunkiest opener blade ever.
A picture of the other side may (or may not) help. Is there a seam where the anchor meets the rope? (exploring the idea of a stuck sheath, with just enough corrosion to make it look like one piece)