A while back, we considered the growing popularity of tattoos as a form of artistic expression. Little did we know HOW popular.

A new study in the scientific journal for skin doctors reports that almost one in four Americans ages 18 to 50 have tattoos. That's 31 million people -- and not just drunken sailors, carnival workers, and lovesick couples -- walking around with hearts and arrows, snake figures, and other designs etched somewhere on their persons.

One of the authors of the dermatologists' study says that in addition to making a "Who I Am" identity statement, "tats," as tattoos are often called, still carry a sort of rebel mystique, not just for biker gangs but for anyone in an era when individual expression is celebrated.

For those clever enough to realize a tat reading "I Love Sally" might not wear so well if Sally departs, temporary tattoos are hot these days, too. There's even a sort of in-between tat -- not permanent, but not easily washed away. The injected ink lasts as long as you want it to -- but can be dissolved using a laser beam.

Even little kids are getting into tattoos -- specifically a candy product called "Tung Toos," which come in 80 images, including a bat, a dog, a soccer ball, and words like "Dude."

They apply the tat by pressing the Tung Too on their tongues and lifting it off while tasting the candy flavor. Then -- to quote the instructions -- they "stick out [their] tongues at [their] nearest friends." According to Tung Toos' president, "kids are able to silently communicate across the classroom without getting in trouble with the teacher for talking." Sounds like something kids would enjoy, all right -- using tattoos and a normally insulting gesture -- sticking their tongues out at a classmate -- to send a secret message.