According to the United States Flag Code, “When the national anthem is played or sung, citizens should stand at attention and salute at the first note and hold the salute through the last note. The salute is directed to the flag, if displayed, otherwise to the music.” Unless a military member in uniform, citizens should stand at ‘salute’ by placing their hand over their heart, facing the American Flag.
http://blog.cvsflags.com/flag-etiquette/national-anthem-etiquette
I bet you half the people in the US couldn't even recite The pledge of allegiance, nor are aware there even is a US Flag Code.
New Law Authorizes Veterans’ Salutes during National Anthem
http://www1.va.gov/opa/pressrel/pressrelease.cfm?id=1609