According to federal law, today is Constitution and Citizenship Day. Congress has helpfully codified the purpose of the day as follows:
"Constitution Day and Citizenship Day commemorate the formation and signing on September 17, 1787, of the Constitution and recognize all who, by coming of age or by naturalization, have become citizens."
36 U.S.C. Code § 106. The statute further authorizes the President to issue each year a proclamation "calling on United States Government officials to display the flag of the United States on all Government buildings on Constitution Day and Citizenship Day and inviting the people of the United States to observe Constitution Day and Citizenship Day, in schools and churches, or other suitable places, with appropriate ceremonies". Id. Although President Trump issued such a proclamation last year, I was unable to locate a proclamation for this year on the White House website.
In honor of Constitution Day, California Secretary of State Alex Padilla yesterday hosted a rare public display of both the English and Spanish versions of the original 1849 California Constitution at the California Museum. Reportedly, this is the first time that the 1849 Constitution has been on public display since 2015. If you missed the display, images of the handwritten English and Spanish versions are available here. The 1849 Constitution was replaced 30 years later by the 1879 Constitution, which has been amended many times in the ensuing years.
Update: This morning, the White House website included this proclamation dated September 16, 2019 honoring Constitution Day.