With one difference. They've added a hashtag.
In 2014, the brand launched its #mycalvins campaign. Enlisted were some of the world's most relevant and influential celebrities: Canadian singer Justin Bieber, model and reality TV star Kendall Jenner, rapper Kendrick Lamar, and hip hop star Fetty Wap, to name a few.
They were instructed to post pictures of themselves in Calvin Klein underwear, with the caption "I ___ in #mycalvin."
Something suggestive normally filled in the blank.
"I think the Justin Bieber thing is brilliant," Calvin Klein, 73, tells CNN Talk Asia
"He's right on. Perfect for now. And Kendall Jenner has a huge following."
The power of social
"Social celebrities" are those with huge clout on platforms such as Facebook, Vine and Instagram. Bieber, for example, has 64.8 million followers on Instagram, while the official Calvin Klein account has 4.3 million.
As these influencers posted raunchy images of themselves in their Calvins, the public began to copy.
Today, the #mycalvins hashtag has been used 362,000 times, with the award-winning campaign touted as one of the most successful uses of social media in advertising.
"It was clear in our new hyper-voyeuristic world that everyone wanted everyone else to see what (social celebrities) were up to in their underwear," says Courtney Blackman, founder and managing director of leading London-based fashion public relations agency Forward PR.
Before Bieber, there was Brooke
If Brooke Shields could have broken the internet in 1981, with the suggestive Calvin Klein ad she starred in that year, she would have done.
The then 15-year-old was filmed writhing on the floor in her Calvin Klein jeans, before murmuring to the camera, "You know what comes between me and my Calvins? Nothing."
The #mycalvins phrase was born.
"Parents were upset," says Klein, "but the people we were trying to reach -- young people -- they were thrilled to have something their parents were upset about."
Controversial advertising became core to the Calvin Klein business.
After Shields followed a now classic black and white ad campaign, shot by French photographer Patrick Demarchelier, featuring both Mark Wahlberg -- aka "the body" -- and Kate Moss, then aged 17, topless.
"I created my own advertisements. I chose the photographer. I chose the models," Klein says.
Back to the future
Today, Calvin Klein the brand it seems has come full circle -- the #mycalvins hashtag being a throwback to those words uttered by Shields.
What does Calvin Klein the man -- who still has financial interests in the company -- make of it all?
"I think they're doing a good job of targeting the market they are after," he says.
"(If social media had been around 13 years ago) I would have used it to my advantage ... and created images that people -- well, their jaw would have dropped."
Crucially, the brand hasn't lost sight of how to monetize on its huge social reach.
The best #mycalvins posts, mostly shot by the public rather than celebrities, are published on a microsite
, which -- of course -- is shoppable.
"The campaign is not far off from the 90s campaign starring Kate Moss and Mark Wahlberg," says Blackman.
"But add user-generated content to the mix via Instagram, Twitter, Snapchat, YouTube, Facebook, and you multiply the visibility to a global audience.
"The campaign has without a doubt cemented Calvin Klein's relevance and influence in the 21st century and has increased its own social media following and sales -- the ultimate goal -- to boot."
What does Calvin Klein do in his Calvins?
As for the man himself, how would he complete the "I ______ in my #calvins" phrase that has gone so viral?
He laughs, and then takes a second to think.
"I mean, I've been in my underwear long before any of them."