It was the Dirty Thirties. Drought and topsoil erosion ruined over 150,000 square miles of Great Plains farmland, and gargantuan black dust storms roiled across the country from Colorado to New York City. Fleeing the Dust Bowl, tens of thousands of farming families from Texas, Oklahoma, and the surrounding states pulled up stakes and headed west.

Meanwhile, a pharmacist from Kansas by the name of Ted Hustead went looking to buy a drugstore and found one he liked in Wall, South Dakota. Unfortunately, Wall's 231 inhabitants didn't comprise a sufficient client base to support Hustead's drugstore. But the lovely Mrs. Hustead had an idea: appeal to tourists headed to the newly opened Mount Rushmore, and to Dust Bowl migrants, by offering them free cups of cold water.

Road signs went up from Minnesota to Montana, printed with the distance to Wall Drug and an advertisement for free ice water.

And the Mount Rushmore tourists came, and the Texan farmers came, and the gold prospectors headed for California came, and soon Hustead stopped worrying about who would buy his wares and started expanding the business.

It grew from a drugstore to a general store, then a department store, and finally became something of a cowboy-themed shopping mall, selling everything under the sun and featuring a western art museum, an animatronic cowboy orchestra, and an elephant-sized fiberglass jackalope.

Today Wall Drug sprawls over 75,000 square feet, takes in over $10 million annually, and during the summer months, they give away 20,000 cups of ice water daily. And it all began with Mrs. Hustead's road signs.

Those omnipresent Wall Drug signs generated so much curiosity and word-of-mouth that it became a major 20^th century meme. 85 years later, both store- and fan-made Wall Drug signs can be found from Afghanistan to Antarctica (talk about selling ice to Eskimos...).

According to Hustead's 1999 New York Times obituary, "American G.I.s...took up the craze and spread the Wall Drug word to the far corners of the world. During World War II it seemed that every sign saying 'Kilroy was here,' was accompanied by one giving the mileage to Wall Drug."

Viral Marketing, 1930s Style

So what made the Wall Drug meme spread like wildfire?

To get to the science behind viral marketing, we wanted to see what the experts said. And one of those experts is Dr. Jonah Berger, Professor of Marketing at the Wharton School at the University of Pennsylvania. In his best-selling book, Contagious: Why Things Catch On, he explores the reasons we're compelled to share ideas and information, and attributes viral success to six key drivers:

Social Currency - People want to share things that support their sense of identity, that tell others they're in the know. Today we might be excited to tell friends we're wearing an Apple watch. During the '30s, you might have been part of the cognoscenti in the same way if you'd actually been to Wall Drug.

Triggers - Easily memorable cues cause us to think, and talk, and spread the word. What makes people want to tell others about the things they've seen and done? What makes something remarkable? Free ice water during the hot, dry days of the dust bowl? That was remarkable. It imprinted itself in the mind.

Emotion - Those curiously enticing signs promised not only relief from the arid, relentless heat, but the scarcity factor (there were way fewer rest stops than today's drivers are used to) created an impelling kind of gotta-have-it longing. And that magical marketing word, "FREE," must have evoked some powerful excitement.

Public - Ideas and behaviors spread when people imitate what they see others doing. Like the big glass jar half-full of bills, sitting on the counter at my local coffee place, which reminds people to tip the baristas. Hundreds and hundreds of signs marking off the mileage must have compelled plenty of drivers to follow the trail to Wall Drug.

Practical Value - We want to share useful info and look good for doing so. "Hey, Aunt Polly. When you're visiting Mount Rushmore, don't miss the ice water at Wall Drug. You'll be glad you made the detour!"

Stories - We love to share information, and what a great story people had to tell about miles and miles of empty highway and the string of signs promising ice cold water at the end of the road...

Dorothy Hustead created an amazingly potent anticipatory buzz 1930s style with nothing more than roadside signs. She didn't for a minute consider herself a marketing guru, but she knew what people would value, and she knew about the power of repetition, and scarcity, and stories that are fun to share.

Of course, back then there were no on-board videos, iPads, cell phones, or satellite radio channels to keep travelers occupied and stave off the boredom of the endless highway - only the alluring promise of those enticing Wall Drug signs.