The statue of Abraham Lincoln looks out over the National Mall in Washington. AP In 1939, the Daughters of the American Revolution refused to let Marian Anderson perform before an integrated audience at Constitution Hall. The Board of Education of the then-segregated District also refused to let her perform in the auditorium of a white public high school. So Anderson turned to a symbol of freedom: the Lincoln Memorial. That April, Anderson held an open-air concert on the steps of the monument to the end of slavery and the ideals of the Republic. Stepping up before a racially mixed audience of more than 75,000, Anderson began with "My Country, âTis of Thee." Two months ago, at the same memorial, a group of students were confronted by a security guard for singing the national anthem. The students, members of the conservative Young Americaâs Foundation, were told by U.S. Park Police that they were "were in violation of federal law and their impromptu performance constituted a demonstration in an area that must remain 'completely content neutral,'" reports FoxNews.com. "The area they were standing in and singing is an area that is restricted for this type of activity," said Sgt. David Schlosser. "The United States Park Police is absolutely content-neutral when it comes to any sort of demonstrations in these areas." One of the students, Shawn Balcomb, said the singing was spontaneous, not planned, and was certainly not intended to be political. "We got maybe two lines in and a police officer came over and he was yelling," he told Fox News. "I was dumbfounded." Evan Gassman, a spokesman for the group, said, "I was taken aback. You wouldnât expect a display of national patriotism to be censored." At that point, he said, it had become political -- and the group kept singing as an act of civil disobedience. "If their idea of civil disobedience is singing the national anthem, then so be it," Gassman said. "Let them disobey."