In the years since the rapper Sisqo (search) sang "Let me see that thong" and fashionistas obliged by letting the undergarment show, things have changed on the lingerie fashion front. These days, thongs are out — or perhaps more appropriately, they've gone back undercover.

Once upon a time, it seemed that nearly every woman wearing low-rise jeans or hip-hugging pants had a thong peeking out the back. What started as anti-panty line underwear became a fashion statement unto itself. It was even hip to adorn the conspicuous G-strings with feathers, beads and plastic baubles.

But in an effort to be less tasteless or more modest, many gals are now tucking their thongs back into their pants and out of sight.

"It's an inappropriate thing to show your thong sticking out," said Elycia Rubin, lifestyle director for E! Networks. "I don't think it looks nice. It's tacky."

Intimate apparel giants like Victoria's Secret (search) offer the popular "boy shorts" as an alternative undergarment. And two fashion designers have sworn off the thong entirely and brought back an older style of underpants with their Visible Panty Line lingerie (search). The pieces include traditional-cut bottoms that can be worn as under or outerwear.

"We are anti the thong," said one of the designers, Victoria Bartlett. "It's on the X list. It definitely should not be seen."

Rubin said the visible-thong trend probably wasn't a deliberate fashion statement at first.

"Because of all these low-cut jeans, it kind of accidentally popped out — unbeknownst to the wearer," she said.

That led to the look becoming fashionable in a daring, rebellious, baring-all sort of way. But now that prim and proper is back en vogue, thong-showing has taken on a tawdry stigma.

"Based on the recent fashion shows and a lot of what we're seeing, right now it's a more modest look," Rubin said. "It's more girly, feminine, refined."

The president of the American Decency Association (search), however, is skeptical that humility really is back in style.

"I haven't noticed any trend toward modesty and I haven't been encouraged," said Bill Johnson. "I look forward to that day, but I have personally seen no evidence of that in fashion magazines or on TV programs."

As for VPL, the lingerie is reminiscent of a more old-fashioned, 1920s and '30s style of underwear with a craftsmanship quality and stitching detail similar to that of the 1950s, according to Bartlett. The 1960s and '70s were also an influence.

"There was the rise of the visible panty lines in the '70s," Bartlett said. "The whole thing was that a visible panty line was a faux pas. But was it a faux pas? We thought there's got to be humor in there somewhere."

Humor — and sex appeal.

"There's something inherently sexy about a visible panty line," said the other VPL designer, Jeffrey Costello.

The VPL pieces are anything but overtly alluring, however.

"It's a little more utilitarian than typically sexy," Costello said. "You have to think about the sexiness of it. But it's not so utilitarian that it's ugly or old-lady."

Regardless, Johnson finds trends like exposed undergarments and visible panty lines troubling — and wonders when and if boundaries will ever be drawn.

"Right now, it may be showing your underwear. I'm very concerned to know what's next," he said. "Numerous corporations are more interested in selling sex than protecting the modesty of our youth. Where is the restraint?"

But E! Networks' Rubin said such fashion fads are in a constant state of ebb and flow.

"It's a cyclical trend — bad girls are in, then good girls are in," she said. "Definitely now, you're seeing a lot more sweetness and playful innocence."