In June, Kamilla Murashova was fined 30,000 rubles, equivalent to about $330, after a stranger traveling on the same train reported her to police for the badges displayed on her everyday red backpack.

One emblem depicted the peace sign. Another said “No to War.” A third pictured a blue sky and a yellow field of wheat—the colors of the Ukrainian flag.

Her offense? Discrediting the Russian military.

The informer had photographed Murashova sitting in the train car, her backpack perched upon her knees with the badges in full display, according to evidence included in documents from the Ostankino District Court of Moscow. He then told the authorities, the documents said.

“I was surprised. I know I did nothing wrong,” Murashova, a 40-year-old nurse, said in an interview. “I didn’t imagine someone would go to such lengths to be patriotic.”

Murashova is one of what researchers and experts in social behavior say are possibly thousands of people who have fallen victim to the proliferating trend of Russians informing on colleagues, acquaintances or people with whom they have only fleeting contact. The practice was commonplace during Soviet times, particularly under the reign of Soviet dictator Joseph Stalin, when people were encouraged to denounce those accused of being “enemies of the state.”

Now “donos,” as it is called in Russian, is gaining traction since the Kremlin ordered the invasion of Ukraine in February last year. Less than a month after the war began, President Vladimir Putin urged people to report anyone who wasn’t fully behind the effort, telling a televised meeting that although the West was trying to split Russian society, “the Russian people would always be able to distinguish true patriots from scum and traitors and will simply spit them out, like a bug that accidentally flew into their mouth.”

“Such a natural and necessary self-purification of society,” he continued, “will only strengthen our country, our solidarity, cohesion and readiness to respond to any challenges.”

Since then, many Russians have responded enthusiastically, reporting anyone deemed to have discredited the Russian military, criticized what the Kremlin calls its special military operation in Ukraine or showed signs of support for Ukraine.

“If the president tells you there are enemies, then you should try to find one,” said Alexandra Arkhipova, a social anthropologist, who has been studying the practice of informing, and now lives in Europe. She said she had been informed on at least seven times.

For some, denunciation is an expression of true patriotism. They view themselves as legitimate whistleblowers, Arkhipova said. Others have been using it to settle grudges by reporting their enemies to the authorities, whether or not they actually are against the war.

Alexei Makarov, a historian for the Russian Nobel Peace Prize-winning human-rights group Memorial, said having citizens inform on each other also helps intelligence agencies track public figures, members of the media or nonprofit organizations.

“If they want to put pressure on an honest activist or organization. How to do it? They find a person who writes a denunciation, and then they say ‘Well, we have received a denunciation, we must look into it,’” Makarov said.

Reports across social media tell of informants who have gone to extremes. A grandmother was reported for planting blue and yellow flowers, a girl denounced for wearing blue and yellow ribbons in her hair, and a man fined after neighbors informed authorities that he was listening to the Ukrainian anthem through his apartment’s open window.

It couldn’t be determined how many people have been informed on since the start of the Ukraine war. But Arkhipova estimates cases could run into the several thousands based on research she and a colleague in the legal field have conducted to track punishments meted out for undermining the Russian military.

Data from Roskomnadzor, the state’s censor, shows the agency received 283,789 reports from citizens in 2022 mostly concerned with “the posting of illegal information on the internet,” including false information about Russia’s military campaign in Ukraine, and requesting its removal, according to information published on the agency’s website. That was more than 25% than the previous year, with the largest jump coming in the month following the beginning of the invasion, though it couldn’t be determined how many complaints came from informants.

“Most often, citizens turned to Roskomnadzor with a request to remove links to resources with pro-Ukrainian propaganda,” the agency said in a report on its website.

“Most likely, we can say that the war in Ukraine and the expansion of the practice of denunciations are interconnected things, because many of these denunciations are related to reaction of Russian citizens to what is happening” [in the war], said Makarov of Memorial, which Russian authorities dissolved in 2021.

“Denunciations are very common now. There are entire groups on the Internet that do this,” Ekaterina Selezneva, a lawyer who represented graphic designer Nina Zolotukhina in a snitching case last year, said in an interview.

Zolotukhina, 24, was detained for two days shortly after the beginning of the war when a man accused her of making antiwar statements in a conversation she was having with an acquaintance at a Moscow nightclub, according to documents from the Basmanny District Court of Moscow. According to the court the man heard Zolotukhina shout “Ukraine will be free! Kill Russian soldiers!”

Zolotukhina denied the charge. In a Telegram message to The Wall Street Journal, she said the man who informed on her was drunk, behaved aggressively and got upset when she wouldn’t pay attention to him.

In January [2023] the court found her guilty of discrediting Russia’s military and fined her 30,000 rubles.

Selezneva, the lawyer, said she had wanted the informer to testify, but the court refused to call him, “as usually happens in political cases,” she said.

Murashova’s lawyer, Anton Aptekar, hit the same obstacle. In an interview, he said he filed a motion to have the man who informed on his client be summoned to the court for questioning, but the judge denied his request.

Murashova admitted that she had the badges described pinned to her bag, but she didn’t plead guilty of the crime for which she was charged because “she didn’t believe that she had done anything illegal,” Aptekar said.

The fact that informers aren’t always required to testify in court allows people to simply make up allegations, according to lawyers who have represented defendants tried on their accusations.

Pensioner Olga Slegina was denounced in December 2022 for complimenting Ukrainian President Volodymyr Zelensky on his looks, according to a report by OVD-Info, a human-rights group that monitors police detentions and helps protesters find lawyers, and which provided Slegina’s defense. OVD said she had called Zelensky “a handsome young man” during banter with another dinner guest.

She was fined 40,000 rubles, according to OVD-Info. Slegina couldn’t be reached for comment.

In March, 40-year-old Yuri Samoilov, a procurement manager, was detained in the Moscow metro after a passenger saw pictures on his phone deemed to discredit the Russian army and called the police. According to documents from the Cheryomushki District Court in Moscow, the screen saver of Samoilov’s mobile phone depicted an emblem of Ukraine’s Azov Regiment. A fellow passenger snapped pictures of it and of Samoilov, who the court ruled to be held in custody for 14 days. Samoilov couldn’t be reached for comment.

Informants have become so widespread that earlier this year State Duma deputy Alexey Nechaev, leader of the liberal New People party described the practice as “an epidemic” and called for legislation that would make “serial informers” liable for punishment.

The Kremlin didn’t immediately respond to a request for comment on the growing number of cases based on informants and whether Russian authorities were encouraging the practice as a way to stop people from criticizing the war in Ukraine or urging an end to the military campaign.

In April, presidential spokesman Dmitry Peskov decried the practice, calling it “disgusting.”

Still, the phenomenon appears to be achieving what analysts said is its intended purpose: keeping Russians in line.

“People believe that denunciation can be everywhere, and from everybody,” Arkhipova, the anthropologist, said.

—Kate Vtorygina contributed to this article.

Write to Ann M. Simmons at