Club Membership Cards
I'll admit that very few people actually check the cards at our field, you always know who the "new guy" is. The thing is as a new guy, you don't know that!
The idea is to reinforce the idea that if you haven't passed the proficiency test at our field yet, you don't have permission to crash your own planes yet! More seriously, we don't want folks up in the air by themselves, out of control, risking our flying site.