Princess Hijab daubs Muslim veils on half-naked fashion ads on the metro. Why does she do it? Is she a religious fundamentalist? And is she really a woman? Angelique Chrisafis meets the elusive street artist

Just after dawn at Havre- Caumartin metro station, Paris's first commuters are stepping on and off half-empty trains. Then, at the end of the platform, a figure in black appears, head bowed and feet tapping with nerves.

Princess Hijab is Paris's most elusive street artist. Striking at night with dripping black paint she slaps black Muslim veils on the half-naked airbrushed women – and men – of the metro's fashion adverts. She calls it "hijabisation". Her guerrilla niqab art has been exhibited from New York to Vienna, sparking debates about feminism and fundamentalism – yet her identity remains a mystery.

In secular republican France, there can hardly be a more potent visual gag than scrawling graffitied veils on fashion ads. Six years after a law banned headscarves and all conspicuous religious symbols from state schools, Nicolas Sarkozy's government has banned the niqab from public spaces amid a fierce row over women's rights, islamophobia and civil liberties. The "burqa ban", approved last month, means that from next year it will be illegal for a woman to wear full-face Muslim veils in public, not just in government offices or on public transport, but in the streets, supermarkets and private businesses. The government says it is a way of protecting women's rights and stopping them being forced by men to cover their faces.

Already this has prompted extreme reactions. One female teacher in favour of the ban was last week given a month's suspended jail sentence for trying to rip a veil from the face of a 26-year-old Emirati tourist in a shop, then slapping, scratching and biting her. On the other side of the argument, two French women calling themselves "niqabitch" reproduced the classic visual mixed metaphor of walking around central Paris in niqabs, black hotpants, bare legs and high heels, posting a film of it online in order to highlight the "absurdity" of the ban.

But Princess Hijab got there first, and her simple, almost childlike acts of sabotage with a black marker pen still manage to be the most unsettling, with the widest audience abroad. Yet who is she? A French Muslim woman in hijab raging at the system? That would be a rare thing on Paris's male-dominated graffiti scene. Is she a religious fundamentalist making a point about female flesh? But she likes to leaves a witty smattering of buttock cheeks and midriff on display. If she's a leftwing feminist making a point about the exploitation of women, it's odd that she always flees the scene of her crimes. Is she even Muslim? Her fans like to imagine a young rebel outsider from Paris's suburban ghettos travelling to the capital to make her mark. But like Paris's greatest street artist, Blek le Rat — who inspired Britain's Bansky — she could turn out to be a fiftysomething white man who voted for Sarkozy.

The Princess winds through the corridors of Havre-Caumartin sizing up the advertising posters lining the walls. She has agreed to meet as she scours stations for targets for her next "niqab intervention". In Spandex tights, shorts and a hoodie, with a long black wig totally obscuring her face, one thing is clear; the twentysomething doesn't wear the niqab that has become her own signature. She won't say if she's a Muslim. In fact, it's more than likely that Princess Hijab isn't even a woman. There's a low note in her laughter, a slight broadness to her shoulders. But the androgynous figure in black won't confirm a gender. "The real identity behind Princess Hijab is of no importance," says the husky voice behind the wig. "The imagined self has taken the foreground, and anyway it's an artistic choice."

"I started doing this when I was 17," she says (I'll stick to "she" as the character is female, even if the person behind it is perhaps not).

"I'd been working on veils, making Spandex outfits that enveloped bodies, more classic art than fashion. And I'd been drawing veiled women on skate-boards and other graphic pieces, when I felt I wanted to confront the outside world. I'd read Naomi Klein's No Logo and it inspired me to risk intervening in public places, targeting advertising."

The Princess's first graffiti veil was in 2006, the "niqabisation" of the album poster of France's most famous female rapper, Diam's, who by strange coincidence has now converted to Islam herself. "It's intriguing because she's now wearing the veil," the Princess muses. Intially she graffitied men, women and children and then would stand around to gauge the public's response; now she does hit-and-runs. "I don't care about people's reactions. I can see this makes people feel awkward and ill at ease, I can understand that, you're on your way home after a tough day and suddenly you're confronted with this."

With the Paris metro protective of its advertising spaces, her work now usually stays up for only 45 minutes to an hour before being ripped down by officials. She has become highly selective, doing only four or five graffiti "interventions" in Paris a year. But each is carefully photographed and has its own afterlife circulating online. The "niqabised" range from Dolce & Gabbana men's underwear to risque adverts for Virgin bookshops.

Why does she do it? "I use veiled women as a challenge," she says, quick to add that she believes no one way of dressing is either good or bad. She's not defending the rights of any group and no one needs her as a spokesperson. "That's paternalistic. If veiled women want to make a point, they'd do it themselves. If feminists want to do something they're capable of doing it on their own." She later explains by email: "The veil has many hidden meanings, it can be as profane as it is sacred, consumerist and sanctimonious. From Arabic Gothicism to the condition of man. The interpretations are numerous and of course it carries great symbolism on race, sexuality and real and imagined geography."

Princess Hijab is deliberately cool and detached, but the one issue that really shakes her – and perhaps reveals a little of her true identity – is the place of minorities in France. Beyond the arguments about whether Muslim women should cover their heads, Sarkozy's new ministry of "immigration and national identity" and his national debate on what it means to be French has stigmatised the already discriminated and ghettoised young people of third- and fourth-generation immigrant descent. France has the largest Muslim population in Europe, but the prevailing anti-immigrant discourse, and what many view as a pointless burqa ban, has increased the feelings of marginalisation felt by young Muslims and minorities.

Princess Hijab sees herself as part of a new "graffiti of minorities" reclaiming the streets. "If it was only about the burqa ban, my work wouldn't have a resonance for very long. But I think the burqa ban has given a global visibility to the issue of integration in France," she says. "We definitely can't keep closing off and putting groups in boxes, always reducing them to the same old questions about religion or urban violence. Education levels are better and we can't have the old Manichean discourse any more."

She adds: "Liberty, equality, fraternity, that's a republican principle, but in reality the issue of minorities in French society hasn't really evolved in half a century. The outsiders in France are still the poor, the Arabs, black and of course, the Roma."

The Princess won't say what her own roots are. She simply says she sees her work as a kind of "cartography of crime" a mapping out of the underbelly of the city where "I bring inside everything that's been excreted out."

And yet her graffiti is particularly French in its anti-consumerism and ad-busting stance. For her, painting a veil on adverts works visually because the two are "dogmas that can be questioned". She feels young women wearing the hijab who were once stigmatised by French institutions are now being targeted for their purchasing power, the "perfect customers" in France's increasingly consumerist society.

Her next spree will focus on her favourite target brand, H&M. After all, its ad campaigns are plastered all over the Paris metro. She argues that the brand "democratised" fashion at low prices, women in hijab often shop there, and inking out H&M models is the perfect act of confrontation: "It's visually very striking because [the brand's] images are ideologically very present in the urban landscape."

So these blacked-out niqabs seem to represent everything but religion. "Am I religious?" she asks, hesitating. "The spiritual interests me, but that's personal, I don't think it bears on my work. Religion interests me, Muslims interest me and the impact they can have, artistically, aesthetically, in the codes that are all around us, particularly in fashion," she muses.

And with that, the graffiti performance artist scuttles off, kit-bag over her shoulder, to change out of her bizarre disguise and into her own everyday fashion and wander off above ground into the daylight.