What about next time?

Now here's a great idea: Take a bunch of electronic boards, put them in conspicuous places all over town, attach them to a couple of bridges.

At first glance, people might think they're bombs or something. But at second glance -- and there's sure to be a second glance -- they'll discover that they're pictures of television characters!

This is the kind of boneheaded thinking that brought much of the city to a standstill yesterday, as law enforcement tracked down 38 devices and Boston learned that one person's ad campaign can be a city's panic attack.

"If you sat in my office [yesterday] you would have seen police cars going up and down the street all day, chasing these devices," Mayor Thomas M. Menino said last night.

He compared it to the city being on terror alert. "They can't perpetrate a hoax like this on the public."

It was good of the Turner Broadcasting people to apologize for their backfired marketing campaign. But it doesn't make it any less unfunny.

"We live in a different world since 9/11," Menino pointed out. "When 9/11 hit, that changed everything."

You know by now that electronic "billboards" were discovered yesterday all over Boston, Cambridge, and Somerville. Some were near major intersections; others were attached to bridges, such as the Longfellow.

The first device was found yesterday morning and soon determined to be harmless. But the anxiety grew considerably as one became five and then 10.

The campaign resulted in an amazing amount of angst caused on behalf of "Aqua Teen Hunger Force," an animated series aired by Turner Broadcasting that most people have never heard of.

On first thought, it might seem as if the mayor and the governor overreacted, that it should have been obvious that these were not explosive devices.

But, as Menino said, that doesn't take into account the way 9/11 permanently altered our sense of security. In that context, erring on the side of caution is the only responsible course to take, and I'm glad law enforcement did too much, rather than too little.

It is interesting that the same marketing campaign is underway in several other cities, including Chicago and San Francisco, without causing the mass freak-out it did here.

Maybe people are less observant there, or perhaps the billboards were planted in less conspicuous locations. That isn't clear yet.

I suspect some people will find what happened amusing, in a Keystone Kops kind of way, and part of me wishes I could join in the fun. But the sight of a city on edge, with local, state, and federal law enforcement on alert, just isn't all that amusing.

It is easy to understand the motivation behind this campaign. It's original, and even without all the drama yesterday it would have accomplished the goal of standing out from the clutter of conventional television advertising.

It was tailor-made for young adults, the primary audience for this type of show.

Still, I wonder what the people who conceived it thought yesterday.

A fuming Menino said he wants a long prison term for the marketing boss behind the campaign and a hefty check from Turner for the expenses the city incurred. Bully for him on both counts.

The events were an extreme collision of pop culture and public safety.

Considering how desperate some media outlets and others are for attention and the lengths they will go to get it, maybe the real surprise is that stunts like this don't backfire more often.

By day's end, amid the civic anger and relief, it seemed oddly possible that the audience for the show will grow, given all the not-quite-free publicity.

Turner got plenty of attention for its show. Boston got a show, too. But it wasn't the kind that makes people cheer.

What lingers is the worry that next time the danger could be real.

Adrian Walker is a Globe columnist. He can be reached at walker@globe.com.