People who do pin trading usually have a lanyard that they can display their pins. Then you can trade your pins with other guests or cast members - but be careful, there's a whole etiquette book on pin trading. Usually, I buy cheap pins, go up to Cast Members and trade the cheap pins for something I like. I have a lot of fun doing that. It's a great way to meet new people.
It's an addictive hobby introduced to the unsuspecting general public by Dangermouse & DLR 29 & other diabolical ride junkies....which is designed to keep families in shops & searching for CMs & OFF our favorite rides.....same thing with Princess Fantasy Faire & the Nemo Ride.