It's not unusual to wear a badge at a convention in the US, whatever that convention may be for. To say there should be no need for a badge to recognise a Christian is silly. I would take off my badge as I was leaving the convention site and so did just about everyone I knew, despite being 'encouraged' not too. One person too afraid to disobey by removing his badge, I remember, would put his coat on over the jacket with the badge, so he was still wearing it but it could not be seen....haha.
If anyone thinks the badge was part of some sinister control plot they need to see a shrink...:)