The letter Z, plastered in white on Mr Kuliak’s white shirt when he received his bronze medal on the parallel bars at a ceremony in Doha, Qatar on Saturday, appeared for those who support the invasion of Ukraine by Russia as a symbol of pride in the attacking armed forces. In the West, it is condemned as a sign of nationalist sentiment.

The International Gymnastics Federation, which on Monday banned Russian and Belarusian athletes from entering its competitions, said it had opened disciplinary proceedings against Mr. Kuliak.

The letter began appearing on Russian tanks and armored vehicles as they massed near the Ukrainian border days before Russian troops crossed the border. Military analysts say the letter, along with other markers, is used by the Russian military as an identifier to distinguish its battlefield equipment from that of Ukraine.

Since the invasion, “Z” iconography has appeared on cars, on banners at pro-Kremlin rallies, and on billboards in Moscow and St. Petersburg subways. At a children’s hospice in the central city of Kazan on Saturday, patients were herded outside to form the letter for a photo op.

In recent days, pro-government videos featuring the symbol have been widely shared on social media. One of these clips opens with a speech in support of the Russian armed forces by Anton Demidov, a nationalist activist, after which hundreds of people gathered in what appears to be a warehouse are shown waving flags Russians and chanting “Russia!” and the name of the president. Vladimir Poutine.

“I don’t know where this symbol came from,” Demidov said in an interview, adding that pro-Kremlin activists saw it on Russian tanks in Ukraine and started using it. “The symbol is not important. position he represents, and that is that we understand that we have to support our president and our army in their difficult task.”

The Russian Defense Ministry and other government institutions have adopted the easily replicable symbol to rally the country around the war, which Moscow has called a “special military operation”.

Shortly after Russia launched the war, state-backed broadcaster RT began selling T-shirts with such phrases. Some companies have replaced the Cyrillic version of Z with the Latin letter in their brand logos, while some government officials have swapped the letters in their social media profiles. In Russian, the word “for” is written “za”, and the Ministry of Defense flooded Instagram with messages saying “for peace”, “for our guys”, “for victory”, all using the English letter Z.

Local governments across the country joined in, lighting up the windows of their government buildings to form the Latin letter Z at night.

“It’s a symbol of people’s unity,” Ivan Zhernakov, an official from the northern Arkhangelsk region who heads its patriotic education department, told state media. “It symbolizes support for our armed forces, support for the president’s decisions, and is designed to unite us in this difficult situation.”

In Ukraine, the symbol descended differently.

Oleksii Reznikov, Ukraine’s defense minister, compared the symbol to Nazi Germany iconography on Monday, posting an image of a swastika-like logo formed of two intertwined Zs that made the rounds on social media Ukrainians. He also tweeted: “In 1943 near the Sachsenhausen conccamp was a Z station where mass murders were committed”, in reference to a Nazi death camp.

The references to Nazi Germany come against the backdrop of Russia falsely claiming that the Ukrainian government is run by neo-Nazis and that one of its war aims is to “denazify” the country. Ukrainian President Volodymyr Zelensky is Jewish.

In Russia, the letter Z was pushed back. A traffic reporter from a public TV channel in Moscow went viral on social media on Monday after telling viewers that if they taped the Z symbol to the rear windows of their cars, they risked more traffic. accidents and being hit by objects. But the letter from the past few days has also been tagged on the property of war opponents.

Russia’s largest human rights group, which chronicled rights abuses in the country before a court forced it to close in December, said on Saturday that security agents had drawn the letter Z in his building after searching the premises.

An activist from feminist punk rock protest group Pussy Riot, which has spoken out against Mr Putin for years, tweeted a picture of the letter drawn on what she said was the front door of her flat.

The claims could not be independently verified.

And Russia’s best-known film critic, Anton Dolin, found the letter on his doorstep before leaving the country. “The message was absolutely clear. The people who did this know that I am against the war,” Dolin said by telephone from Latvia. “They showed that they know where I live and where my family lives. It’s an act of intimidation.”

Mr. Dolin said that for him, the letter is less reminiscent of Nazi iconography and more of a popular zombie movie. “It’s reminiscent of World War II,” he said, referring to the 2013 Hollywood film starring Brad Pitt and based on a book of the same name. “I see him as representing our zombified army and the zombified part of the population that watches state television and supports the operation.”

His children, he says, see another meaning in the symbol: Zlo, or Russian for evil.