Autumn Light includes a small icon to the left of each menu item.
This icon will not be automatically added to each menu item you add. You'll need to manually add this icon to the individual menu option each time you add something new. You can do this in the ProPhoto menu system under ProPhoto 4 --> Customize --> Menus --> Primary navigation menu:
Hover over the menu item you need to edit, then click the gear icon to open the menu item properties:
Choose "text & icon" and select "to the left of text" as the alignment. Upload the image named "post_icon.png" (you can find this icon in the "Original PNGs -- For Your Reference" folder. Click "Save Changes..."