How do I add an icon to a page menu link in page menu bar?

I would like to put an icon in my page menu links. I am using a page menu bar at the top of the header and figured out how to stylize the text and background color. What I want to do now is put a 15x15 px icon to the left of the titles in this bar.

Is there a post here that already covers this topic?

my site in development is at:
http://depts.washington.edu/ophthweb/wordpress/

I want to put the icons in front of the links at the top of the page.

Thanks in advance,

Bill