Here's another one: I put my full name and some other identifying information on the lock screen of my phone*. They won't be able to unlock it, but just looking at the screen they'll know who I am if they're trying to ID me.
*this one worked for me during a military deployment once too. I had my phone in my pocket and went to take care of some business, ahem, and about 20 minutes later I got an email from someone saying they had my phone. It had fallen out of my pocket while my pocket was, uh, lower than it's usual level.