I believe it is in horrible taste...IMHO, bordering on insulting. My own opinion, and it may very from those of others on this board and that is fine, is that since it was radical islamics that did the killing that day...acts of war...then we should not attach any symbol remotely resembling their own onto the memorial honoring our dead, and in this particular case, our heroes as well.
I am of the same mind myself. I don't believe that it is appropriate to incorporate the symbol of Islam in this memorial to Americans who were defending themselves -- and America -- against radical Islamists.