Photo: Send me 5

This key [in a photo I took about a week ago] was attached to a pole at the intersection of State Street and South U.


The post-it note behinds it reads:

I found your
key, you are
welcome
[street address]
Send me 5.

which I can only assume means $5. Who does something nice and then tacks up a note asking for $5?

I kind of want to send the person a letter and find out. Except I would need a not-me address the person could write back to.