The correct option is SYMBOL.
A symbol refers to an object or character which is used as a conventional representation of an object, process or function. Symbol is a thing which stands for another thing.
In the question given, the flag stands for United States of America.
Iceberg is the writing style of Hemingwat. Influenced by his journalistic career, Hemingway contended that by omitting superfluous and extraneous matter, writing becomes more interesting. He summarized his theory:
If a writer of prose knows enough of what he is writing about he may omit things that he knows and the reader, if the writer is writing truly enough, will have a feeling of those things as strongly as though the writer had stated them. The dignity of movement of an ice-berg is due to only one-eighth of it being above water. A writer who omits things because he does not know them only makes hollow places in his writing.