Add Caret to Menu Items with Sub-Menus in WordPress Theme

Question

I'm working on a custom theme using wp_nav_menu(). What I want to do is add a caret to menu items that have sub-menus. For example, If my menu looks like this:

• Menu Item 1
• Menu Item 2
  • Menu Item 2a
  • Menu Item 2b
• Menu Item 3

I want to be able to format it like this:

• List item
• Menu Item 1
• Menu Item 2 >
  • Menu Item 2a
  • Menu Item 2b
• Menu Item 3

Without knowing the structure of the menu. This seems like a pretty common formatting problem, so I was wondering if there is any built-in functionality to provide for this.