This is something I did not know about previous to reading this proclamation.
As part of the normal defense authorization legislation in 2008 signed by George W. Bush, a section was included to authorize commemoration of the 50th anniversary of the Vietnam war. The first event was held at the Vietnam War Memorial Wall on May 28, 2012.
This proclamation is a continuation of the commemoration that is to go on for 13 years.
I found this site useful for more detail.
Official Title and Link: Presidential Proclamation Commemorating the 50th Anniversary of the Vietnam War
Proclamation dated November 10, 2017