Oh, it's a landmark, all right. But it's NOT visible from the anywhere you can sail, and since you don't see landmark names when you're walking, that bit of information is almost meaningless.
Here is the solution, in case anyone else is ever unlucky enough to get that thrice-accursed map. In the strictest sense, it IS 'northwest of Gran Grenada', but that's rather like saying 'Los Angeles is west of the Mississippi'. Not very accurate at all.
If you go to the southwestern corner of the Bay of Honduras, there's a little pirate outpost on the southern edge. If you walk just slightly southeast from there, you'll find the spot (almost straight south, just ever so slightly to the southeast). The body of water doesn't show up on any of the maps, which is rather stupid. I basically found the spot by blundering into it after a loooooooooong search.