Here are a couple of ideas:
http://readingacademy.monroe.edu/course/view.php?id=85 http://www.dreamstime.com/stock-photography-open-book-vector-symbol-image1774182http://www.easyvectors.com/browse/other/old-book-clip-artI just did a quick search for "clip art knowledge" and "clip art book" to come up with these. I'm sure you, as the professional, can develop something that will work and still show the cool E and S. I really like the idea of the key unlocking knowledge...
Thanks!