If Procter & Gamble Co. Chief Brand Officer Marc Pritchard wants ad viewability, he's getting it, right from the windows of his corporate headquarters.

In response to Mr. Pritchard's speech last week to the IAB Annual Leadership Meeting on the problems of digital ad viewability and fraud, among other things, the Outdoor Advertising Association of America has put up six billboards near P&G headquarters in Cincinnati shouting out: "Hey Marc, This ad is real."

The Cincinnati effort revives the OAAA's "Feel the Real" campaign originally introduced in 2015, which went on hiatus last year in favor of a pro bono voter-registration effort. Lamar Advertising donated the space for the new Cincinnati campaign, including a prominent spot along the on ramp to a major thoroughfare heading east from P&G headquarters that's been used in the past by such rivals as Unilever and Church & Dwight Co. to tweak P&G marketers.

The new ads are 100% viewable by their target audience for as many seconds as he cares to look. P&G spokeswoman Tressie Rose confirmed that Mr. Pritchard had seen the one nearest the headquarters. She added: "We agree. The ad is real."

The campaign was created by Partners & Napier in Rochester, New York, a Project Worldwide agency.

The ads direct curious onlookers to campaign website FeeltheReal.org. The first wave of ads included 1,500 placements in 15 markets nationwide targeting 50 ad agencies, often in billboards or transit shelters near their offices and sometimes calling out individual agency executives or creative directors, said OAAA Chief Marketing Officer Stephen Freitas.

The idea isn't entirely about poking fun at viewership problems of digital media. It's also meant to portray out-of-home as "a perfect complement to the digital space, because it's out there in the real world and can help guide you to some of that digital content," Mr. Freitas said.

But then, when news of Mr. Pritchard's speech hit last week, the OAAA also welcomed the opportunity to point out that its medium has few viewability issues, he said. "It's also a great use case to say look at how targeted out-of-home can be."

Billboards might seem like a blunt instrument to reach Mr. Pritchard plus maybe his fellow P&G marketers. But the OAAA wouldn't be the first to give that a go in the headquarters city of the world's biggest ad spender.

Billboards that went up largely in neighborhoods surrounding downtown last year bearing the Snapchat logo were aimed at least in part at catching the eye of P&G marketers, said a person familiar with that campaign.

Similarly, Radiocentre, the trade group for U.K. commercial radio, targeted rival Unilever Chief Marketing and Communications Officer Keith Weed, who oversees the world's second biggest ad budget, in radio ads there last year.