Ephemera for the month of May seems appropriate.
This is a Harper & Brothers Form No. 802 which was placed in each box of books packed for shipment. Printed on the reverse are lines for the initials of the individuals who packed the box and checked the box after packing. Their quality control of the day.
If you are visiting New York you may want to check out the exhibit at Columbia University: Caterers General to the Literary World: The House of Harper (Chang Octagon, RBML, Butler 6th Floor East, 535 West 114th Street) March 28 through June 30, 2007. It was mounted to coincide with the Bibliographical Society of America’s conference: Birth of the Bestseller: The 19th Century Book in Britain, France, and Beyond which ran from March 29th to the 31st.