Well the one I have is a Foreign Language Certification Pin. It goes under a CMs name tag and has a flag from the country that speeks the certified language (ex France flag for French, spain's flag for spainish etc.)
But as far as guest pin trading goes... Its really just a fun activity for guests and cast to interact with eachother. I trade some but its only for pins that mean something to me. I am a HUGE MGM fan so I collect pins from MGM. There are some hardcore Pin Trading fans out there though that only really collect pins of value. I am not like that but they are out there, and in fact I think most people are like me and trade just for fun.
If you have any other questions about pin trading you can always ask!
~Ali