When Jessica Clary visited Los Angeles as a teenager with her mother in 1995, the attraction they were most excited to see was not the Hollywood sign or Rodeo Drive. It was the courthouse where O.J. Simpson stood trial for murder.

Ms. Clary, who grew up in Plano, Texas, said that like millions of Americans, she and her mother became transfixed by the case then described as “the trial of the century.” On the day the women went to see the courthouse in downtown Los Angeles, they were not the only people on the streets outside. Several vendors had come to hawk merchandise.

“We bought a ‘Dream Team’ shirt for my dad,” Ms. Clary said, using a phrase adopted as a nickname for Mr. Simpson’s lawyers. “I got a ‘Free the Juice’ button,” she added, using a nickname for Mr. Simpson, who was found not guilty.

Ms. Clary said they didn’t buy the products as a way to communicate opinions on the trial. The merchandise was meant to commemorate an event that she described as “such a big part of pop culture.”

Though Mr. Simpson’s trial was not the first to draw outsize attention, its coverage in newspapers, on television and on the internet helped pave the way for modern true-crime entertainment. And, like his trial, many legal spectacles since have inspired scripted programming as well as merchandise.

During the case over Britney Spears’s conservatorship, which a judge terminated in 2021, the hashtag #FreeBritney was plastered on coffee mugs and T-shirts, one of which was worn by Ms. Spears. Other people whose legal affairs have spawned merchandise include Anna Sorokin, the fake heiress better known as Anna Delvey; Elizabeth Holmes, the Theranos founder awaiting prison; and Jen Shah, a star of “The Real Housewives of Salt Lake City,” who went to prison after pleading guilty to participating in a fraudulent telemarketing scheme. (Before she pleaded guilty, prosecutors said, Ms. Shah sold T-shirts inspired by her case.)

In March, Ms. Clary, now 44 and living in Los Angeles, started an Etsy store that sells trial-related merchandise. Among its items are mugs and T-shirts inspired by the case of Alex Murdaugh, the South Carolina lawyer convicted of murdering his wife and son, that say “Murdaugh Family Law.”

There are also clothes inspired by Gwyneth Paltrow’s recent ski crash trial in Park City, Utah, in which the actress was found not at fault for a collision on the slopes. Some of the pieces say “Gwynnocent,” while others feature Ms. Paltrow’s now famous quote from the trial: “Well, I lost half a day of skiing.”

Ms. Clary, a fund-raiser for the Coast Guard Foundation, designs the pieces using the software Canva. Her products typically cost between $25 and $35. The Etsy store, she said, is a modern version of “people with folding tables in front of the courthouse.”

Chantal Strasburger, 32, who lives in Austin, Texas, has also sold merchandise inspired by Ms. Paltrow’s trial. Her pieces include quarter-zip sweatshirts ($65) embroidered with the actress’s skiing quote and baseball hats ($30) that say, “I wish you well,” which Ms. Paltrow was overheard telling her accuser after the verdict was delivered.

Ms. Strasburger, who featured the products in a TikTok video that has received almost two million views, said she had sold more than 400 since she started offering them through her embroidery business, Read Receipts. She thinks customers appreciate the merchandise because it nods to a specific moment in time. “They want to capture that moment,” Ms. Strasburger said, “and immortalize it forever.”

Tara Ann Stridh, a 43-year-old writer in Queens, said that when she bought a hat inspired by the defamation case between Johnny Depp and Amber Heard, it was mostly a gesture of support for Ms. Heard, who lost the trial. The baseball hat, which Ms. Stridh bought on Etsy for $25, read, “Believe Amber.”

“I thought, Well, I can’t contact her and I’ll just buy this for myself because I want to support her,” Ms. Stridh said.

Lorynn Divita, an associate professor of apparel merchandising at Baylor University, described trial merchandise as an evolution of band T-shirts and other trinkets sold at concerts. These types of products, Ms. Divita said, can be a way for their owners to show off their cultural awareness and interests.

For some, even the possibility of a trial is enough to fire up the screen printer.

After the Justice Department appointed Jack Smith as special counsel overseeing its investigations into former President Donald J. Trump, Scott Horner, 53, worked with two graphic designers to create merchandise that included $25 T-shirts with Mr. Smith’s face alongside phrases like “Mr. Smith Goes to Washington” and “Somebody’s Gonna Get Jacked Up!”

Mr. Horner, a travel agent in Orlando, Fla., started selling the products online last December. He said he has since sold about 1,500 and that he would not be surprised to see other people start hawking similar merchandise as Mr. Smith’s work ramps up.

“I think there’s going to be definitely more interest if there are trials,” Mr. Horner said.