Tomorrow is the 6th anniversary. Every year since 9/11, the Congress has declared Sept. 11 "Patriot Day" and the President has issued a proclamation calling for all Americans display the flag at half mast.
Since most flags designed for home use are not designed to fly at half mast, a black streamer can be flown with the flag.
Austin
I fly a 3'x5' flag almost year round.
I also fly a flag year round - except during football season. On game days, we switch it to a Titans flag (most of the time).
Our American flag and black streamer went up at daylight......