Faulkner employes italics as a visual clue for the reader. What does this form of punctuation always signal in "Barn Burning"?

This question is more complicated than it sounds. Even though Italics are usually pretty reliable to indicate a break with the narrative in general (they may indicate an internal monologue for instance), a lot depends on who has edited the text.Italics are not a form of punctution like commas or hyphens, but a change in font that denote a change in the pattern of expression.

Especially when it comes to Faulkner, publishers and editors have tackled his writings in different ways. I think one can only answer this question in a careful and comparative fashion by looking at the publication of a certain text and by comparing it to Faulkner's original. Most of his publicicized works keep his Italics, but some insert different forms of punctuation ( Absalom,Absalom for instance).

That being said, there is no sure way of reading Faulkner's Italics.