Visitors to Riverside High School in Kanawha County have to sign in first. That's nothing new.

But school officials said the white sticker that visitors have to wear turns bright blue or purple if they step outside.

The change in color identifies potential troublemakers to teachers and other school personnel.

Parents have to wear the tags, too, but they like the added security.

"If the kids steal them or try to take 'em out and try and get their friends to come in and sign them out, they're not going to get out?" asked Riverside parent Lisa McClure.

The answer: That's right. Stickers exposed to daylight automatically change color, thus alerting school personnel the pass is dated.

The school has a public library, bank and health clinic, so people are coming and going all the time.

Riverside High School has used the stickers for several years.

The school pays $250 for 2,000 stickers.