They do seem to be the symbol--which makes sense in terms of visual thinking, because the damage to the Pentagon was repairable, and planes have crashed in fields before. The other visual effect is a lot harder to reproduce on a poster in a way that will make the connection--the empty skies, for a few days during the "total ground standdown," a weird thing to see in a major city with as many airports as we have.

Those weren't especially loved buildings, as architecture or for long history, but they were familiar to a lot of people, from movies and television even when not from real life. Coming into the city from Queens in the couple of years afterwards, I would find myself glancing at the skyline, to make sure the rest of it--and in particular the Empire State and Chrysler Buildings--was still intact.