People don't really wander around downtown Manhattan with bombs or assault weapons. If they're looking to bomb GS, figuring out GS is at 200 West is unlikely to be the greatest of their challenges. (There's few ways it could be more public than being listed in their Wikipedia infobox.)
I don't claim it makes any sense, but after 9/11 one of the things that JP Morgan did was remove their name from many of their buildings in the UK.
I agree that most people don't have assault weapons or bombs. "Blogger Bob" shows what a few people take into airports (many training grenades, which look real to scanners and cause delay). It's surprising how many people try to take loaded handguns onto planes.
They did in the 1920's the first ever car bomb (a horse drawn cart) was used against the NY stock exchange. I belive you can still see the shrapnel scars on the buildings facade.