This is from a photograph I took from a WWII era book.  During WWII everybody did their part to help with the war effort.  This included publishers who had to print books on a lesser quality of paper.  This stamp is an indication of a book that uses war paper instead of the higher quality of paper that was used prior to WWII and in the following decades of the 1950's and 1960's.  

There is a constant War of Ideas going on in a Democracy.  Books are weapons in our arsenal to combat the misinformation we sometimes find on social media and elsewhere on the internet.