Citing an FBI informational document, ABC News reports a so called "battle of suspicious bags" is being encouraged on a jihadist website.
Bomb expert Kevin Barry with 20 years experience in the NYPD says the bags could be filled not with bombs, but with innocuous items like water bottles or socks.
Your humble blogger was all over this ages ago:
What the city of Boston...has shown the terrorists is that all you have to do to sow fear and chaos is leave some strange objects scattered around high-profile areas. That's it. You don't have to smuggle uranium or anthrax. You don't have to take the risk of manufacturing explosives. You could fill 20 Jansport backpacks with old phone books, have people drop them at 20 subway stations simultaneously, and probably keep every emergency responder in the city tied up for at least an hour or two.
And then you could do some real damage.
(H/T for link and graphic above to Thoreau)