The black T-shirt spells it out in capital letters: “Everyone Watches Women’s Sports.”

In the past few months, the message has been hard to miss. Dawn Staley, the coach of the University of South Carolina’s women’s basketball team, kicked off a social media frenzy when she wore the shirt for a pregame interview in January. The comedian and actor Jason Sudeikis wore a version with yellow lettering to the women’s N.C.A.A. tournament finals in April. Jimmy Fallon got one on “The Tonight Show” as a gift from the recently retired W.N.B.A. star Sue Bird.

The shirt, which was created by a company co-founded by Ms. Bird, has become an unofficial uniform as viewership of women’s basketball has soared, and women’s sports in general have seen greater momentum.

Megan Ramos, 25, saw more than a dozen of the shirts at a W.N.B.A. game last month. “Shipping is a little behind,” said Ms. Ramos, who ordered hers in April, “because everyone wants them.”

The short-sleeved shirt, which sells for $45, was introduced last December by Togethxr, the media and apparel company created in 2021 by Ms. Bird, the soccer player Alex Morgan, the swimmer Simone Manuel and the snowboarder Chloe Kim. (A hoodie is also available for $85.)

The slogan aims to turn a common jab against women’s sports on its head. “It’s a play on people saying, ‘Nobody watches women’s sports’ — like, John590 from Twitter with no profile pic,” Ms. Bird told Mr. Fallon. “Now the numbers show it, which is amazing, so now we actually have data to it. Actually, everyone watches women’s sports.”