I'm confused

In the mail today I found two interesting pieces of mail:

1. A thank you note from Marilyn, my Allstate insurance agent, for refering Jason to her for motorcycle insurance. I thought it was very nice of her to send a hand written thank you card. I really like her. Everyone should use her. She rocks.

2. An envelope with no return address and my first name spelled wrong. It also lacked the apartment number, but had the right house address. I didn't recognize the handwriting on the envelope and the postmark said Grand Rapids. It was mailed on Friday. So I open the envelope to find folded notebook paper. I unfold it and out falls a five dollar bill. The notebook paper is blank. No note. No name. Nothing. Just $5.00. I'm confused. I've been pondering it all afternoon/evening. I don't get it. I'm just baffled.

Okay, so who sent me $5.00 and why?