Seeing the horrible news today about suicide bombers killing so many people and wreaking so much havoc in the Moscow subway system makes me feel very vulnerable once again riding the New York City transit system. There are so many entry points, and only so much the police can do to secure them.

It's common to see cops on duty checking the occasional backpack, some with the help of bomb-sniffing dogs, at the busiest stations. And I am still taken aback at the sight now and then of a member of the National Guard, in full combat gear, brandishing rifles at a subway entrance that almost look like toys. Still, you can't help but conclude that it's mostly for show.

Yes, there are cameras everywhere, but that's more for after the fact, isn't it? Just who is watching, anyway, and how might they pick out an individual threat before it's too late?