I thought it would be fun to look back at the history of the National Library Symbol which was adopted in 1982 at the ALA (American Library Association) conference. We have this symbol on our book drop outside. Working in the library field, I have seen this symbol displayed in many places and in many ways and I recognize it immediately. However, like anything, if you have not been “introduced” you may not know about it!
The National Library Symbol, which depicts a generic human figure reading a book, was originally designed by Ralph E. DeVore for use in the Western Maryland Public Libraries. The ALA Presidential Task Force on a National Library Symbol specifically sought a standard symbol that could be used to identify all types of libraries, hoping to increase public awareness of the institution of libraries.
Through the years, people have had fun rethinking and reworking the original symbol. I really like the one I have inserted here where a family is reading together!
In 2015, for summer reading, I challenged students to rework the symbol using superheroes. Here are a couple of fun examples of what were submitted then. 
Citation: https://www.ala.org/ala/alalibrary/libraryfactsheet/alalibraryfactsheet30.htm