Most intuitive accordion action icon

1. Which of the following accordion signifiers is most likely to signal to users that the accordion will open in place rather than leading to a new page?
2. Which way do accordion arrows go?
3. How do I add an icon to my accordion?

Which of the following accordion signifiers is most likely to signal to users that the accordion will open in place rather than leading to a new page?

Summary: The caret icon most clearly indicated to users that it would open an accordion in place, rather than linking directly to a new page.

Which way do accordion arrows go?

Arrow Conventions

Trees have used right-pointing arrows for closed and down-pointing arrows for opened, which, as FreshCode mentions in his answer, has been generalized to expanders.

How do I add an icon to my accordion?

Open the Accordion module settings and go to the Advanced tab. Go to the CSS IDs & Classes toggle. Place the class “pa-add-accordion-icon” in the CSS Class input field.