Tonight, "South Park" opens up its thirteenth season with the Jonas Brothers passing out purity rings to Kenny and his girlfriend.

What's the latest accessory to grace the bodies of teens wearing barely-there skirts and tummy-bearing tops? Purity rings. Selena Gomez, the star of "Wizards of Waverly Place," wears one on her left ring finger that says: "True Love Waits." Jordin Sparks defended hers on the VMAs. The Jonas Brothers don silver metal bands to signify their promise to God to remain virgins until marriage. And now the Joe Bros. are even passing them out on "South Park!"

"American Idol" winner Jordin Sparks says of her ring: "My parents gave me a purity ring and talked to me about waiting until I'm married to have sex. It wasn't forced; it just made perfect sense. It's going to be awesome to say to my husband that I waited my whole life for him."

Sociologists found more than one in eight American teens have made a virginity vow to God. The good news: Studies have shown that purity pledges lower the risk of early sexual activity and teen pregnancy. The bad news: Researchers have also found that girls who make purity pledges were six times as likely to engage in oral sex than virgins who hadn't taken a pledge, and were also less likely to use a condom the first time they go all the way.

What do you think of purity rings: good idea or just another stupid trend?