But don't be surprised if you see ones that are completely unrelated. Don't get pins confused with buttons. A pin is made of thick metal and attached with a military clutch. This means a sharp point goes through the cloth and has a separate unit holding it on. Buttons are made of a flimsy, soda-can like metal with a picture glued to it and covered with plastic, and have a long pin that goes into the cloth and comes back out to reattach to the main unit.
Pins are normally smaller, heavier, prettier, and more valuable.
There are several different kinds of pins. The cheapest ones are plastic ones. For instance, many people last year had green Heinz pickles. While they were pretty, they had little real trading value. Don't trade too much for these, but if you see one you like go for it.