Revealing mistake: After Jonny Lee Miller gets shot in the head, he slowly falls into the water, facing Sara and Gabe. In the next shot, he has turned towards the water. If you watch closely, you can also see him turn his head so he doesn't hit the face on the water surface. (01:34:15)
Revealing mistake: When Gabe fights with Lucas, if you look closely the entire time "Lucas" is actually a stunt double.
Chosen answer: Vince explains this. The letters spell out CROATOAN. There was an English colony on Roanoake Island, of which the entire population mysteriously disappeared, giving no trace of what had happened, barring the letters CROATOAN carved on to a tree.