Tisha b'av night, I went to hear Eichah at the home of someone in the apartment building I lived in for the past few months. I brought my siddur with me to daven ma'ariv. Inside my siddur are various pieces of paper with different tefilos on them. The next morning, I noticed that I was missing one of the tefilah cards from my siddur, but didn't think too much of it since I figured it was lost somewhere in my apartment.
The day after the fast, I was reading the daily digest of the building's frum listserve, and I noticed that the host for the Eichah reading had posted a message saying that he found a Chofetz Chaim tefilah card in his apartment, and judging by the location where he found it, he assumed that one of the women had left it there. I immediately realized that it must be mine, and emailed him to tell him so. He very graciously agreed to drop it off at the building's front desk so that I could pick it up at my own convenience.
When I went to pick it up, the tefilah card was in an envelope clearly labelled with my name and apartment number. This man didn't even know me personally, but he went and made the whole transaction convenient for me. Thank you!