I thought the message to be very powerful. So I wanted to find where this sign is / was located.
All I found was:
In 1917, at 49, {William Tyler} Page wrote the "American's Creed," as a submission to a nationwide patriotic contest suggested by Henry Sterling Chapin, of New York, which was inspired by a fervor at the beginning of the American entry into the First World War.
http://www.ushistory.org/documents/creed.htm also see: https://en.wikipedia.org/wiki/William_Tyler_Page
by William Tyler Page
I believe in the United States of America as a government of the people, by the people, for the people; whose just powers are derived from the consent of the governed, a democracy in a republic, a sovereign Nation of many sovereign States; a perfect union, one and inseparable; established upon those principles of freedom, equality, justice, and humanity for which American patriots sacrificed their lives and fortunes.
I therefore believe it is my duty to my country to love it, to support its Constitution, to obey its laws, to respect its flag, and to defend it against all enemies.
–Written 1917, accepted by the United States House of Representatives on April 3, 1918