I noticed something that I think was a mistake. About two minutes into the show, Leonard has just walked through the taping of "Sheldon Cooper Presents Fun With Flags." Of course, Sheldon is upset, so Amy asks him if he's okay. He tells her that he is not okay, that he's a little rattled, "but, like the flag over Fort Sumter , I'm still here." Now, isn't that a reference to the Star Spangled Banner which Francis Scott Key wrote about the flag flying over Fort McHenry (not Fort Sumter ) in 1814? When Sheldon says "I'm still here," that has to be a reference to the phrase "that our flag was still there" in the anthem.
Of course, Fort Sumter was the site of the first battle of the Civil War and the Fort Sumter Flag is still on display at the National Park Service, but I'm not aware of any stories about the flag that would be understood by the "viewers".