First off, WELCOME TO THE DIS!!
Now, the lime green ribbons are for identification purposes. If you are a member of the DIS Boards and are at WDW, most of us wear a lime green ribbon (or the new lime green Mickey head from Home Depot's paint department) so that other members will know that we are on here and we can strike up a conversation or just say hello. It is a good way to put a face to a username you may have seen here on the boards and make new friends. Does that make sense?