What was he only clue that John white discovered about he missing settlers when he returned to he Roanoke colony?

The Word "Croatoan" was carved on a post at the entrance to the palisado, and a similar "CRO" was carved on a tree. A secret sign that the settlers were forced was no inscribed anywhere.

(The best explanation was that the settlers went to live with nearby Indian tribes, and were lost to accident or attacks.)