In early September Marlene Rivera, a photographer in Houston, made an announcement on Twitter. “Ladies we are no longer dressing up as sexy cops,” she wrote. “Our new sexy costumes are mail carriers.”

Ms. Rivera, 24, never misses a chance to dress up on Halloween. In recent years she’s transformed herself into an astronaut, Wonder Woman and Supergirl.

Her festivities this year will be more low-key. She and five friends are planning a night of board games and drinking adult beverages outdoors at a friend’s beach house in Galveston, Tex. They will still be wearing costumes, and because of the pandemic and fraught political climate, she wants her choice to send a message.

Ms. Rivera feels as strongly about the costume she won’t wear as the one she will. “Wearing a police officer costume is no longer appropriate,” she said, before adding that she would be a mail carrier. “I felt this was an opportunity to show appreciation and express the importance of mail-in ballots for voting.”

This has been quite the year for postal workers. They’ve gone from unsung heroes in the perpetual shadow of the UPS Guy in “Legally Blonde” to applauded front-line workers. Some have gained fame on Instagram or had beers made in their honor. Now they are being saluted in another way: Americans planning to dress up as mail carriers for Halloween.

Ms. Rivera bought her costume from Amazon, where there are a handful of options. Her kit includes a vest, cap, mail storage bag, even letters with stamps on them. She is going to wear the costume with a skirt and knee high boots to make it sexier.

Other Americans are buying mail carrier costumes straight from the source: the United States Postal Service. For $24.95 you can get a costume for a child or toddler; one for a dog that has attached arms that carry a priority mail box costs $17.99. “Initially, we offered a limited quantity of the costumes, which sold out and were replenished,” said Sara Martin, a spokeswoman for the Postal Service.

Caitlin Galeotti, 28, a publicist who lives in the Carroll Gardens neighborhood of Brooklyn, couldn’t believe the post office sold Halloween costumes.

“After reading about U.S.P.S.’s financial crisis and how consumers can help, I went on their website to do my small part by stocking up on stamps,” she wrote in an email. “I quickly learned they sell more than that.

“I’m not usually the type to dress up pets, but as soon as I saw the U.S.P.S. costume, I knew I wanted to get it for Cleo,” Ms. Galeotti said, referring to her dog, whom she plans to take with her to drop off candy at local post offices. (She also bought herself a crop top sold on the same website.)

Meryl Pataky, 37, a sculptor in Oakland, Calif., bought a costume for her 50-pound pit mix, Oscar, even though only one size, extra small, was left. “I bought it anyway,” Ms. Pataky said. “I felt that was a really cute way to show and give my support.”

Taanya Spates, 27, who has worked as a mail carrier in Charlotte, N.C., for almost six years, is not surprised that her uniform is suddenly a hot costume.

Ms. Spates has an Instagram account, Puerto_Rican_Pecan, on which she posts pictures of herself working. She drives a mail truck to a residential neighborhood and then walks five to six miles every day to complete her deliveries. Before the pandemic she would get around 400 likes per picture. Now, she gets 60,000.

“I think a lot of people were at home, and they weren’t doing much, and essential workers got highlighted,” she said.

And Ms. Spates appreciates the coming homage, though she herself will be a butterfly this year.

“I wouldn’t dress up as a mail carrier for Halloween because it’s my career, but it’s super-flattering,” she said. “We work all year, during rain, sleet, snow and now literally pandemics.”