Plenty of businesses try to boost their credibility by displaying logos of media outlets that have done stories about them. A mention on CNN, for example, is a badge of honor that can build credibility among wary consumers.

Which media logos do the best job reassuring potential customers that a business is legit? One online service recently ran interesting experiment to find out. (Hat tip to MediaWire for the heads up on this study.)

Thumbtack.com, which hooks up service providers with people in need of service, concluded that logos from the New York Times, the Washington Post and the Wall Street Journal boosted conversions among the general public. The familiar blue-and-white USA Today nameplate actually hurt business.

Thumbtack did A/B testing on separate landing pages aimed at consumers and service providers (house cleaners, handymen, pet sitters, etc.). The Washington Post and the Wall Street Journal boosted conversions for both sets of users. The New York Times did great among consumers, but didn’t do well among the service providers.

USA performed poorly among both groups, actually driving down conversions. In other words, Thumbtack’s call-to-action pages hooked more users without the USA Today logo than with it.

In its post explaining the results, Thumbtack said, “We have no idea why this hugely popular newspaper would have decreased conversions across the board. Your guess is as good as ours.”

So here’s my guess: Even after all these years, USA Today comes across as a lightweight media brand. The paper marks its 30th anniversary next year, but it’s still seen as something of a freebie. You know, the newspaper you see laying around the boarding area at the airport or the paper you find waiting for you outside your hotel room door.

Some of the knock against USA Today is unwarranted. The paper’s reporters have done great work over the years. One notable example was USA Today’s work in 2006 exposing the National Security Agency’s efforts to compile a gigantic database of Americans’ private phone calls. USA Today’s entertainment and sports pages have been good over the years, too.

USA Today ushered in a new era of graphic design among newspapers — punchy layouts, quick reads and lots of color graphics. In some ways, USA Today’s bold look and bite-size morsels of information were a precursor to what we’ve become used to on the web.

In recent years, of course, USA Today has been beset by many of the same problems plaguing newspapers across the nation. Revenue losses have forced staff reductions, which in turn have hurt the quality of the product.

Way back when, I was part of endeavor mocking USA Today. In December 1991, the staff of the Minnesota Daily put out a USA Today spoof called the U of M ToDaily. We packed almost story with bullets and tweaked the familiar “Snapshots” feature with a tagline of “A look at stats that don’t really matter.” Not long after the issue came out, we got a letter from USA Today lawyers telling us to knock off the knock offs.

Maybe we were on to something even back then. USA Today is the paper millions of people read, but few truly love.