Novapress uses icons provided by Font Awesome in its menu.
To add an icon to the menu items or change the existing icons, follow these instructions.
In the Admin Panel go to APPEARANCE > Menus.
Select Screen Options from the top of the screen and check CSS Classes.
You will now see a CSS Classes field appear in each menu item.
Enter fa and the class of the icon which you can get from the Font Awesome Cheatsheet.