Long lines of voters formed outside polling stations in major Russian cities during the presidential election on Sunday, in what opposition figures portrayed as a striking protest against a rubber-stamp process that is certain to keep Vladimir V. Putin in power.

Before he died last month, the Russian opposition leader Aleksei A. Navalny had called on supporters to go to polling stations at midday on Sunday, the last day of the three-day vote, to express dissatisfaction with Mr. Putin, who is set to win his fifth presidential term in a vote that lacks real competition.

Mr. Navalny’s team, which is continuing his work, and other opposition movements reiterated calls for the protest in the weeks leading up to the vote. Simply appearing at the polling station, for an initiative known as Noon Against Putin, they said, was the only safe way to express discontent in a country that has drastically escalated repression since its full-scale invasion of Ukraine two years ago.

The opposition leaders said showing solidarity with like-minded citizens by mere presence was more important than what the voters chose to do with their ballots, because the election lacked real choice.

“This is our protest — we don’t have any other options,” said Lena, 61, who came to a polling station in central Moscow before noon with the intention of spoiling her ballot. “All of us decent people are hostages here.” Like other voters interviewed, she declined to provide her last name, for fear of reprisal.

Alissa, 25, said she came because she is against the war. “It is so important to see people who think like you, who don’t agree with what is happening,” she said.

Initially proposed by an exiled former regional Russian lawmaker, Noon Against Putin became a rallying call for Russia’s embattled opposition after the death of Mr. Navalny in an Arctic prison last month. His widow and political heir, Yulia Navalnaya, has presented the initiative as a way to honor his legacy and protest his death, which she blamed on the government.

“You saw each other. The world has seen you,” Leonid Volkov, one of Mr. Navalny’s chief aides, wrote in a note on social media thanking supporters who came out at midday. “Russia is not Putin. Russia is you.”

Mr. Volkov hosted a live broadcast of the vote on Mr. Navalny’s YouTube channel earlier on Sunday and wore a sling on his arm. He was taken to the hospital last week after being beaten with a hammer outside his home in Lithuania, a reminder of the dangers faced by the opposition, even in exile.

The nature of the midday initiative makes it virtually impossible to estimate just how many of the people who came to the polls at that time came with the intent of registering a protest. More broadly, the muted, purely symbolic form of civil disobedience envisioned by the initiative underscores just how little the Russian opposition can do to influence events in the country amid the pervasive repression.

The government has vowed to punish attempts to disrupt the vote. And a Russian human rights and legal aid group, OVD-Info, said more than 60 people had been detained across Russia by 3 p.m. in Moscow on Sunday for actions related to elections.

Despite the risks, all five voters consulted by The New York Times outside one polling station in Moscow said that they came to express their support for Mr. Navalny. “According to the Russian Constitution, the source of power is the Russian people,” said one voter, Kristina, 22, as the noon bells of a nearby church sounded. “We are supposed to be the ones with power here, but unfortunately in our country the person in power is a murderer. He killed our Lyosha,” she said, using a nickname for Mr. Navalny, for whom she had once worked as a volunteer.

Kristina later sent a photograph of a ballot she said she had spoiled before depositing it in the ballot box. It had the words “Navalny, we’re with you,” written in capital letters across the candidate choices. Shortly after that, she was briefly detained by the authorities, who she said had asked her why she “spent so long” standing near the polling station.

Long lines were also seen at Russian embassies in countries with large Russian diasporas. Noon Against Putin has been expected to be particularly large-scale abroad, because dissident voters faced lower risks outside Russia.

Ms. Navalnaya was seen standing in a long line outside the Russian Embassy in Berlin on Sunday afternoon. And around the same time, several hundred voters formed a line outside the embassy in Riga, Latvia, despite the document checks carried out by local police. The government of Latvia has called Russian elections a sham, and has tried to discourage its large ethnic Russian population from participating in the vote.

Tomas Dapkus and Anton Troianovski contributed reporting.