Related Rule
United States of America
Practice Relating to Rule 100. Fair Trial Guarantees
Section C. Presumption of innocence
David Hicks, an Australian citizen, was captured in Afghanistan in December 2001 and afterwards detained at Guantanamo Bay Naval Base, Cuba. In March 2007, in the Hicks case, the accused became the first person to be tried and convicted under the US Military Commissions Act of 2006. Following a pre-trial agreement struck with the Convening Authority, the accused pleaded guilty to the charge of “providing material support for terrorism”. In April 2007, Hicks returned to Australia to serve the remaining nine months of a suspended seven-year sentence. In the case’s record of trial for the 26 March 2007 hearing, the military judge stated:
It is also standard practice that an accused will not appear for a trial session wearing prison garb. That would refer to jumpsuits or scrubs or things of that nature.
These rules, as I would expect counsel probably know, are designed to protect the presumption of innocence on the part of the accused. The rule with regard to not appearing in prison attire is for the protection of the accused such that the court or commissioned members or a jury depending on what jurisdiction you are in, the people that are making findings with regard to guilt or innocence, would not be inferring anything adverse on the part of the accused based on them wearing some sort of prison or jail clothing. So again, this rule of court is there to buttress the presumption of innocence that an accused is afforded in these proceedings. 
United States, Office of Military Commissions, Hicks case, Record of Trial, 26 and 30 March 2007.
According to the Report on US Practice, “Articles 4, 5 and 6 [of the 1977 Additional Protocol II] reflect general US policy on treatment of persons in the power of an adverse party in armed conflicts governed by common Article 3” of the 1949 Geneva Conventions. The report also notes: “It is the opinio juris of the US that persons detained in connection with an internal armed conflict are entitled to humane treatment as specified in Articles 4, 5 and 6 [of the 1977 Additional Protocol II].” 
Report on US Practice, 1997, Chapter 5.3.