Sia performed on “Saturday Night Live” in January wearing a black tulle mask over her eyes. The singer has said that her decision to hide from the camera is a matter of self-preservation. (Dana Edelson/NBC)

Last month on “Saturday Night Live,” the singer Sia was in the building. And yet, in a strange sleight of hand, she wasn’t.

Her pipes were certainly there, their own life force, growling and bending into her trademark ear-splitting wail as the Australian singer belted out “Elastic Heart.” But Sia herself was a shadowy presence, turned away from the audience, her eyes hidden behind layers of funereal black tulle.

On Sunday, the megahit-generating songwriter is up for four Grammy awards, including record of the year and song of the year, for her maybe, possibly addiction-recovery anthem “Chandelier.” She’ll also perform during Sunday’s telecast — and when she does, the big question won’t be what Sia will sing but how Sia will sing it.

Will she don the frilly black visor from “SNL” again? Or the dumpy paper bag that she wore on the cover of Billboard magazine? Or perhaps she’ll simply turn her back on the tens of millions who will tune in, as she did last year on “Jimmy Kimmel Live” and “Ellen.”

Whatever she chooses, the one sure thing is that we won’t see Sia, because Sia doesn’t want to be seen.

It’s a head-scratching attitude in a world where most celebrities eagerly bare all to their audiences and TMZ. You can’t help wondering: Is her retreat from the camera and touring genuine? Is she being eccentric? Or is the paper bag just another Hollywood gimmick?

If Sia’s goal is to shun fame, it’s ironic that she’s more famous now than she’s ever been.

Online commenters are calling the singer’s choice to cover her face “weird.” Perez Hilton has referred to it as a “quirk.”

Sia, who is up against artists 15 years her junior on Sunday, says it’s self-preservation.

In the “manifesto” she penned for Billboard when she reluctantly returned to recording two years ago, she compared fame with an insufferable mother-in-law, prying and poking until there was no boundary left uncrossed. Take that mother of a metaphor, she wrote, “and apply it to every teenager with a computer in the entire world. Then add in all bored people, as well as people whose job it is to report on celebrities.”

With her back turned to the “Nightline” cameras last summer, Sia hinted to ABC’s Chris Connelly that her experiment was a reaction to the rise of the troll, the hate tweet, the well-meaning but sexist think piece. “I don’t want to be critiqued about the way that I look on the Internet,” she told him flatly.

The dance-music duo Daft Punk also perform in face-concealing headgear (Danny Moloshok/REUTERS)

“We level a lot of violence at celebrities,” says Kate Durbin, a Los Angeles-based performance artist and cultural critic. “Turning your back to the audience is kind of like giving them the finger, like ‘You’re not going to do that to me. You’re not going to destroy me.’ ”

It’s no secret that women have the worst of it with the pop-music microscope. Just do a search for Sia’s fellow Grammy nominee Meghan Trainor and brace yourself for the chorus of subtle fat-shaming.

But rather than leave singing to those with a more Instagrammable thigh gap, the 39-year-old Sia — who, for the record, showed her face publicly for most of the 10 years that she has been a bankable name, baring her smile to the crowds at South by Southwest and spending a season cheesing for cameras as an “adviser” on NBC’s “The Voice” — now navigates the spotlight on her own terms. By sidestepping the spotlight entirely.

Even the cover of the album “1000 Forms of Fear,” her first in four years, offers only the singer’s now-iconic weed-whacked blond wig floating on a shadowy sea of black.

And she’s not entirely alone: Beyoncé donned a fishnet mask for last year’s “On the Run Tour” performances, and in the recent video for “Superpower” she pulls on an even more militant balaclava, not unlike the ones that members of the Russian band Pussy Riot used in 2012 when they stormed a Moscow cathedral. Lady Gaga has been hiding and revealing, presenting ever-stranger public incarnations of herself, for years.

But in the case of Queen Bey, says Rutgers University lecturer Kevin Allred, who’s famous for teaching an undergraduate class called “Politicizing Beyoncé,” the masks aren’t so much to hide as to highlight the singer’s carefully managed, picture-perfect veneer.

“We never see Beyoncé, really,” Allred says. “We’re never privy to any moments, even in the documentary she put out. Those are pre-planned, packaged private moments.” If the public insists on total transparency from celebrities, Beyoncé has mastered giving only as much as she wants, he says, creating false intimacy. As with the fishnet, “she’s guarded,” Allred says, “but you can still see through it.”

Of course, men have hidden behind masks, too. For his 2013 “Yeezus” tour, Kanye West obscured his ferocious glare beneath a series of bejeweled Maison Margiela stocking masks. Dance-music duo Daft Punk have removed their visages from the equation — and the discussion around their music — by wearing glam robo-helmets for the better part of their career, offering that the disguises are both part of their performance art and that beneath the helmets they’re not so hot to look at. Dance act SBTRKT and rockers Slipknot, Kiss and Gwar mask, too.

But the message that’s sent when female performers cover their perfectly contoured cheekbones and rouged lips seems twice as significant, especially when they say they’re feminists. It’s art, subversion, gimmick and gender politics all rolled into one.

“I like the idea of reading it as a refusal to play into the kind of pressures and misogynistic ways, and what the entertainment industry forces women to be to be popular,” Allred argues. Sia’s live appearances, he says, make audiences uncomfortable, “but in an interesting way, because it does pose these questions.”

On the other hand, Durbin says, in covering her face, Sia may actually be triggering more commentary; fans, she says, are left to fill in the blanks not only about what she looks like, but also about what it means. “She’s not giving anything of herself, except her back.”

For the record, Sia isn’t quite giving her audiences nothing: She offers 12-year-old dancer and reality-TV veteran Maddie Ziegler and, on occasion, models, men and even Lena Dunham in blond wigs as her stand-ins.

So, has this new approach harmed Sia’s career? Notably, the video for “Chandelier” has racked up more than 500 million views; “1000 Forms of Fear,” the singer’s first No. 1 album, still lingers on the Billboard and iTunes charts nearly 30 weeks after its release.

“It could also be argued that her concealment is precisely the attention grabber,” says Mathieu Deflem, a professor of sociology at the University of South Carolina, “because, intended or not, it works that way.

“After all, who would the public want to see more than the one who refuses to reveal herself?”