And after the fall, he would take it out and run his finger along the edge until the paper started falling apart. There were water stains around the bottom edge and spattered up the right hand side. The paper got so thin he eventually couldn't take it out of his wallet anymore to look at. Sherlock found it when he was poking through John's wallet just before the wedding, stained and nearly torn in two. He keeps a copy of it in his mind palace.