h/t JW Rawles:
I believe our flag is more than just cloth and ink. It is a universally recognized symbol that stands for liberty, and freedom. It is the history of our nation, and it's marked by the blood of those who died defending it." - Senator John Thune
US Flag etiquette. While Emily Post-style "dealing with other folks" etiquette is a matter of custom and courtesy, flag etiquette is a matter of law.
Flag Day is also the US Army's birthday: