Death's flag is the flag flying above Old Glory when the nation is in mourning. No, you can't see it, but at least you're thinking about it, and that's the whole point of the American flag being at half mast.
The tradition dates back to the 1612, when the British ship Heart's Ease arrived in Canada with her captain dead. When it next arrived in London, its Union Jack was at half mast, making room for the invisible flag of death.
Whitney, we hardly knew ye . . .
The flag was lowered nationally for Pope John Paul II, Neil Armstrong, Rosa Parks, Winston Churchill, Anwar Sadat, Yitzhak Rabin and Nelson Mandela. It was also lowered to mourn the shootings in Virginia Tech, Newtown, Conn., and Charleston, as well as for the Boston Marathon Bombing and the Indian Ocean Tsunami in 2004.
Governors of the states, territories, and the Mayor of Washington, D.C. also have the authority to lower the flags in areas under their jurisdiction.
If you can't lower you flag because its in a fixed position on the pole, the American Legion advises you to put a black ribbon to the top of the pole.