I have my Camera Club Membership Card attached to my camera bag, and I've been debating whether or not to glue a business card onto the back of the camera itself. In the meantime, I put a business card in the bag.

When I first started working, my boss advised me to keep a business card in the pocket of whatever type of coat I was using that might be checked or hung up on a coat rack; that has saved a coat twice--once when I left it at a restaurant & once at church when someone took the wrong coat. That latter incident also taught me to always to hang a coat at either end of a coat rack. People may not always remember exactly where in a rack they hung a coat or know to where it got moved, but they do remember that it wasn't at the end so they are more careful to insure the coat at the end is really theirs.