Remember these?

School assembly. Lindsey, a cute tween redhead, takes stage behind microphone. Applause.

Lindsey: "Today I'm going to talk about Patty."

Pan to Patty, who smiles timidly from behind glasses.

Lindsey, matter of factly: "Patty's best characteristics? She's stupid. Stupid and ugly."

Patty grimaces.

Lindsey: "Look at her. Greasy hair, dirty fingernails. It makes me want to vomit."

Pan to devastated Patty.

Flashes on screen: "If you wouldn't say it in person, why say it online? Delete Cyberbullying. Don't Write it. Don't Forward it."

This 30-second commercial - like so many other Advertising Council campaigns featured in an exhibition at the Art Institute of Philadelphia - not only reflects today's social issues but also creates a powerful force for change in our popular culture.

When did seat-belt use become de rigueur? Credit the Crash Test Dummies. Why does everyone know the term designated driver? Thank the public service announcement that told us true friends don't let friends drive drunk.

And now, cyberbullies beware. Advertisers, government agencies and nonprofits have joined forces once again in the hope that textual harassment will stop - and eventually become a habit as unimaginable as not wearing a seat belt.

"Any cultural product is a fingerprint of the time in which it was made," said Robert Thompson, director of the Bleier Center for Television and Popular Culture at Syracuse University.

Consider the PSA slogans and images seared into the minds of whole generations: "Loose Lips Sink Ships." "A Mind Is a Terrible Thing to Waste." "The Toughest Job You'll Ever Love."

I remember that is a familiar refrain when PSAs are discussed. A walk through "Advertising That Changed the Nation," which runs At the Art Institute through April 3, conjures a visual timeline of America's societal concerns over nearly seven decades, from "Rosie the Riveter" to the current "Think Before You Speak." (The latter takes aim at homophobic language such as "That's so gay.")

Together they reflect the changes and constants within the American public - bits of history done in the haiku of adspeak. They provide "a direct listing of the fears, pathologies, concerns of a culture," Thompson said. "It's a way of reading priorities and agendas of any given time."

How do these messages come to life? And why do some become icons of the times?

Consider one of the council's most memorable campaigns: the "Crying Indian."

In the 1950s, as the nation's highway system grew, more families took driving vacations. With that phenomenon came the widespread habit of throwing trash out car windows.

Some concerned citizens, realizing the damage to the environment from litterbugs, formed the nonprofit Keep America Beautiful. A PSA campaign was the obvious vehicle to raise awareness, and in 1961, the anti-littering group partnered with the Ad Council.

Early ads featured "Suzy Spotless" scolding her litterbug dad, and pigs rummaging through people's litter.

But American attitudes and culture really began to change after the Marsteller ad agency created spots that featured actor Iron Eyes Cody, canoeing in a river littered with trash as a single tear rolls down his disappointed face. Launched on Earth Day in 1971, the ad became synonymous with environmental concern and was credited in large part with stimulating wider interest in environmentalism.

At the height of the campaign, Keep America Beautiful received more than 2,000 letters a month from people who wanted to join the effort, according to an Ad Council report on its most effective campaigns. By the time the award-winning campaign ended in 1983, litter had been substantially reduced in hundreds of communities across the country, the report said.

Similarly, the Peace Corps campaign ("The Toughest Job . . ."), launched in 1961, soon attracted more than 30,000 people to the volunteer program, and the slogan "A Mind Is a Terrible Thing to Waste," begun in 1972, has helped the United Negro College Fund raise more than $2.2 billion.

One of the original campaigns, "Rosie the Riveter," urged women to get jobs as men left for battle. After she told women "We Can Do It!" - a challenge to gender roles - two million women entered the workforce, according to the Ad Council.

PSAs like these "appeal to our better angels," said Tim Reeves, CEO of the Harrisburg-based Neiman Group, whose Philadelphia office is the sponsor of the Ad Council exhibit. "Sometimes, all people need is a nudge."

The New York-based Ad Council - a nonprofit that joins ad agencies, organizations, and media outlets to deliver messages pro bono - has made nudging its mission. It adopts only issues that seriously affect the nation and have solutions that involve individual action. Results must be measurable.

Fifty campaigns - taking on issues as diverse as adoption, emergency preparedness, and arts education - are currently underway, said Paula Veale, a spokeswoman for the council.

An advisory committee of academics, corporate leaders, and council officials selects five to 10 campaigns a year, she said. Also, each presidential administration since the council's founding in 1942 has had favorite causes that reflected the times.

The Renew America Together campaign, launched in January under the auspices of the Obama/Biden Presidential Inaugural Committee, urges Americans to take personal responsiblity and help change their communities.

Commitments to campaigns can run for years. "We know it takes a very long time to change a social norm," Veale said. Still, "it's the way so many people are getting really crucial information on so many issues."

The icons, like all good advertising, grab the attention - often by tugging at emotions such as fear - and thereby endure.

They "go for the jugular," Thompson said. In one popular anti-drinking and driving ad, two beer mugs are raised high in a toast, but instead of a joyful clink, brakes screech and glass shatters. The 1990s tagline - "Friends Don't Let Friends Drive Drunk" - became the most recognized anti-drinking-and-driving slogan in America, according to a council survey.

Increasingly, humor has taken hold - an acknowledgment, Thompson said, that the public can be cynical about sales pitches.

Vince and Larry, the Crash Test Dummies who have failed to buckle up, chatter wryly as they plunge violently into the windshield during a crash. "You could learn a lot from a dummy," the tagline reads.

What's this decade's iconic PSA? It may never have one. The diversity of media - not just three major networks but hundreds of cable stations and Internet sites - makes it harder to achieve that status. The council now also spreads its messages via blogs, YouTube, Facebook, and online games in the hope of reaching new generations and changing behavior - and ultimately our culture.

Herve Charlot, 23, a graphic design student at the Art Institute, recently marveled at the staying power of the classic Smokey Bear, who turns 65 this year.

"I wish I thought of Smokey," he said. "You can only hope for a design that takes hold and affects a generation."

To learn about current campaigns, as well as watch PSA commercials, go to www.adcouncil.org/default.aspx?id=15.