ExposeTheMedia.com seems to have discovered the first genuine “dog whistle” of the 2012 campaign: an anti-Romney ad by the Obama campaign that features, and zooms in on, a “Breitbart Is Here” t-shirt.

A dog whistle is a secret political signal meant to be heard only by a section of the audience. Here, the signal–if it is, indeed, an intentional one–is probably missed by most, but likely to be picked up by Obama’s left-wing fans, who make no secret of hating Breitbart.

The short ad attacks Mitt Romney for a joke he told last week about the controversy over Barack Obama’s birth certificate. It’s a form of guilt by association, attempting to link Romney with the conspiratorial Birther movement. 

That message seems to be reinforced by the focus on the Breitbart t-shirt, particularly for the left-wing audience at which the ad is largely aimed, and which is more likely than the general public to have heard of, and to have been outraged by, allegations that Romney is following the Breitbart playbook.

The mainstream media and the Obama camp have accused the Romney campaign of using racist or sexist “dog whistles”–including the joke featured in the ad. However, as Matt Lewis of the Daily Caller notes, none of Romney’s alleged dog whistles have been “heard” by conservatives: “The whole point [of] a dog whistle is for your adversaries to not hear it. It should go over their heads, and straight into the ears of your base…Why is it that liberals are the only people who hear the conservative dog whistles?”

The Breitbart t-shirt is possibly a genuine liberal dog whistle, meant to link Romney with Breitbart–and everything the left hates about Breitbart. The Obama ad also could be interpreted as implying that the woman wearing the t-shirt behind Romney must have been placed there by the campaign. In fact, as she proudly announces on her blog, she carried out her own plan to slip into the camera frame as a tribute to Breitbart.

Of course, it just as likely that the Obama ad’s oblique focus on the Breitbart t-shirt is pure coincidence. But the left has thrown tantrums at the Romney campaign over far less, including the bland slogan “Obama isn’t working.” As Breitbart predicted in February, this has become the left’s “dog whistle” election. So–game on.