It's a safety product. Comes in wrist band, ankle band, shoe tag, or dog tag. It has your name and emergency contact along with medical info like allergies. It's great if you're riding alone or with a group that doesn't know you and you're injured. I don't ride alone much, but my partner mountain bikes alone a lot so it makes me feel better that she wears it in case something happens.

Here's a link to the site: http://www.roadid.com/Common/default.aspx