The roundup of convention ideas is here.
When I was at a Project Management Institute meeting some time ago, the people doing the badges added a neat extra; colored tags indicating job status. There was one sticker indicating your company was hiring, one indicating you were seeking work. The "seeking work" stickers outnumbered the "hiring" ones, sadly, but it was a great idea.
Of course, at conventions, people are always putting things on their badges – stickers, ribbons, tags, etc. They personalize them to show off their interests, affiliations, or just for the sake of fun. I see a lot of it in the Bay Area.
You probably see where I'm going with this.