I came across them for one of my advent calendars on the blog. I read on several sites that it was an old English Christmas tradition that got lost in the 20th century, but with people picking up old traditions again instructions are easy to find, not just on British sites.
"In 18th century England there were "kissing balls", balls of mistletoe decorated with ribbons, evergreens and ornaments. Young ladies standing under such a kissing ball could not refuse a kiss. If a lady remained unkissed, it meant that she would not marry the next year, indeed people even avoided her saying she would probably stay an old maid."