The security guard picked up my wallet and gave it back to me. The property asked me to write a thank-you letter and send a banner. What should I do?

Think about how you would feel if you didn't have property to force you to write a letter of commendation. When the security guard finds the wallet and turns it in, he may not always think about praise. It's just that property leaders want to use this matter to expand their influence. After all, what you do in the end is up to you, and no one can intimidate you into doing what you don't want to do.