A contextual symbol is a symbol whose meaning is not widely recognized by a society or culture, but that can only be recognized within the context or framework of a specific story because these are unique symbols that authors created to serve a certain purpose in the story.
An example of contextual symbol is the White Whale in the Moby-Di.ck novel by Herman Merville, that is said to represent God, the divine or nature as it is powerful and can not be tamed or beaten. This character works as a contextual symbol because it can only be recognized as such by the readers of the novel.