Jamie Tzioumis, 35, a chef and yoga instructor from Brooklyn, still wears her button, but she also aggressively makes sure commuters are aware of her situation — she will stick her belly in their faces, she said.

She has also learned the power of strategic button placement.

“Sometimes I’ll put it on my breasts,” said Ms. Tzioumis, whose first child is due in January. “They’re getting bigger, so they’ll grab some attention.”

While pregnant riders can at least hope that their bodies might be enough to prompt a polite response, many disabled riders, another population targeted by the button campaign, say that is not always the case for them.

Shannon Barnsley was thrilled when she first heard about the button campaign on a Facebook group for New Yorkers with invisible disabilities, which include chronic illnesses and other conditions that may not be physically apparent, but still make it difficult for people to stand in a shaky, crowded subway car.

But when the yellow “Please offer me a seat” button arrived in the mail, Ms. Barnsley, 28, was immediately unsure of whether it would help people understand why she might ask for a seat. There was no mention of disabilities on the pin, said Ms. Barnsley, who has postural tachycardia syndrome, which leads to lightheadedness and seizures.

“I feel kind of awkward using it,” she said. “Part of the problem with invisible disabilities is people aren’t aware of them, so the button not really making anyone aware of it doesn’t really help.”

Ms. Barnsley said part of the issue might be that she has not seen any public service announcements explaining the purpose of the buttons. She compared the campaign to a similar one on the subway in London, which she has seen on social media and that the transit authority has cited as inspiration. In London, Ms. Barnsley said, the transit agency clearly included invisible disabilities in its campaign. The buttons, which have the same wording as the ones in New York, come with cards that say, “Remember, not all disabilities and conditions are visible.”