You probably don’t know Monica Poli’s face, but you might recognize her voice. Deep, booming and coming from your phone during a late-night TikTok scroll.

“Attenzione, borseggiatrici! Attenzione, pickpocket!”

Ms. Poli, 57, who lives in Venice, has become prominent on social media for patrolling the streets of her hometown, calling out would-be pickpockets to tourists.

She is part of a group known as the Cittadini Non Distratti — the undistracted citizens — who wander the city shouting at people whom they believe to be thieves plucking wallets, passports and other items from the pockets of passers-by.

Sometimes Ms. Poli and her fellow amateur watchdogs will report these suspected pickpockets to the police. In 2019, The Economist reported that the group was responsible for a third of all pickpocket arrests made in Venice.

The civilian group has been active for decades but only recently joined TikTok and Instagram, where hundreds of thousands of people now follow along, thanks in large part to Ms. Poli’s unmistakable voice. Her shouts of “Attenzione, borseggiatrici! Attenzione, pickpocket!” have become a meme. (She has even been remixed, her voice front and center in a dance track.)

In a typical video, Ms. Poli films a crowded area, like the city’s train station. Then she begins shouting. In some clips, the suspected pickpockets can be seen fleeing from her lens. Others who have been seemingly caught in the act will hold up bags or hats to hide their faces.

If you’re watching these videos with headphones, you’ll want to turn the volume down: Ms. Poli has to be loud enough to get the attention of not only the supposed wrongdoers, but also tourists.

In a recent interview, Ms. Poli, a lifelong Venetian, discussed her sudden brush with internet fame and why she’s still out roaming the city’s streets after all these years. The conversation has been edited and condensed.

How long have you been doing this?

We are a group of about 50 persons. The first time we caught a pickpocket was in Venice about 30 years ago. I think it’s the first group in Italy. The oldest.

Are there other anti-pickpocket groups?

In Milan. I think there is one in Rome. In Spain, Barcelona.

Why did you join social media?

We opened TikTok and Instagram to let the people of the world know that when you come to Venice, be careful.

How often do you patrol the streets?

Depends. Sometimes all day after work, because I work in the morning. I clean offices. After, I spend my time protecting the tourists. It can be three, four, five, six hours.

What do you look for?

They stop in the station. The way they look at people, the way they look at bags. I have a sixth sense.

Are you ever concerned that you’re calling out a person who is not actually a pickpocket?

No. When I see them, I know they are pickpockets. It is so strange to say … I have something inside me and I recognize immediately.

This morning, I was on the bus to Venice. From the bus, I see two men and one woman in the street. I had never seen them before. I went out from the bus and I caught them. I look at the woman and she has a bag open. There were two police, and I say, “Stop them!” They were pickpockets. In one minute, they stole wallets from three families.

Have the police ever asked you to stop?

No, never.

How do the pickpockets react? Do they ever get violent?

There was an episode about five years ago. Four girls fought me, and people stopped to see the scene. I was alone. People stopped to see the action and never helped. It was terrible. I had a neck collar for 20 days.

Did that make you want to stop?

It doesn’t matter. I will continue to do this work.

Do the pickpockets recognize you? Do they know to run away from you now?

They recognize me. The men, they affront me with the middle finger. They take pictures of me. The girls, they run away. I think they think I’m crazy, maybe?

You are famous on TikTok now.

It was so strange for me. My voice is everywhere! I am happy because the message arrived where we wanted. We want the tourists, people coming to Venice and Milan, to pay attention. The pickpockets are so quick.

Have any tourists started recognizing you?

This morning, I was in the street and a tourist looked at me. He said, “You are … ‘attenzione, pickpocket!’” He was with a little girl. I said, “Yes.” “I found you! Can we take a picture?” He was from Denmark, I think.

How do tourists react when you start shouting? You are impressively loud.

At first they look at me for a few seconds, and then they watch what happens. “Attenzione, borseggiatrici!” After, they say thank you, because they understand.

Tourists, particularly American tourists, don’t have the best reputation. Why defend them?

I protect all the tourists. Tourism in Italy is very important. We live with the tourists. I want people who come to Italy to have respect, and we must respect them.