Just to add on to what gypsy said, you can get permanent or non-permanent cards. I'm never going to take my mare to rated shows, so rather than spending all the money and effort (she's a hony ;) ) to get an "official" pony card at some big recognized show, she just has one from our county show organization. It only works for those shows, but that's all I need. Depending on where you're showing, you may not even need a card. Local/schooling shows will often times just take you at your word unless there's a big question about size.
Worth The Wait <3