That has happened a few times to me in the last couple of years, it is really good when it happens.
Years ago, i saw the nephew of an old friend of mine i hadn't seen for 25 years. I wrote my mob. no. on the back of an old sign i put up in my properties to stop unwanted guests entering hoping he would pass it on to Jules.
Months later he had lost this piece of paper with my no. but he walked past on of my properties and saw the sign, he remembered it and waited for a resident to turn up. I was shocked when i met up with him later that day.