Check out this article in the Yale publication "Working@Yale", featuring the Valentine's heart formed on February 14th by Yale Library staff:

http://working.yale.edu/whos-news/library-staff-get-heart-matter

The heart signifies that the library staff are indeed at the heart of all the Library does, while echoing the engraving on the wall outside the front entrance of Sterling Memorial Library that states "The Library is the Heart of the University".