Instead of seizing and lauding the deaths and "achievement" of the terrorists, memorialize the "let's roll" area in the sky.
"Seize" and honor the area in the sky and make it a NOTAM no-fly zone memorial that pilots can mention over the intercom as passengers fly next to it.
Perhaps it is because THAT is where the unrecovered remains, remain..
Alternatively, the government could seize the number '93' to memorialize United Flight 93. All counting and mathematical processes would go from 92 directly to 94, unless you were in possesion of a special licence, obtainable from the government for a fee, (the proceeds of which would be allocated to the Special Government Task Force for Studies of the effectiveness of memorial fees)
I guess we shouldn’t have graveyards either.