If you lost your cell phone and an honest and helpful person found it, could they get it back to you? If you’ve filled out the owner information, and if your cell is not password-protected, probably yes. If your phone is protected, though, the finder might not be able to get to the owner information. The same logic applies to cameras, calendars, paper-based address books, and planners. A phone number on the inside cover, or inside battery cover (Sharpie), is usually accessible to anyone who would take the trouble to find an owner.
Don’t use your cell number on your cell phone.*
I found a well-used planner in the exit lane of our office parking lot once, where it had fallen after its person had placed it on the roof of the car and forgot it. It had six weeks of future appointments and no owner information. Because it was clear it belonged to a Realtor®, I left it at the front desk of (one of) the attorneys’ offices in the building, in hopes that the owner had a) been at a closing and b) would remember the last stop. Never heard.
A return address label in the front, along with a cell phone number, would have solved that problem much faster. One of my friends adds a “reward for return” note next to her phone number.
*I have a friend who locked the keys to a padlock ON the hasp of the padlock… For sure, he never lost the keys.
20091109 Update: In the process of packing up my PC to carry it to a convention, I wondered how many other people might have the same model (few, but this is a theoretical thought). Then I realized I had no identifying information ON my PC itself! Oops! Added an address label with my phone number on the bottom of the case, and another inside the battery pack, and one in the laptop sleeve, and on the charger. I’m certain I’ve missed something, but I’ve covered what I can think of at the moment.