There are plenty of pieces of information you could put on an ID tag, some of them highly effective, some of them potentially dangerous, and of course, you have limited space. So, what should you include?
Your name is necessary, for starters. Most people will want you to identify yourself as the correct owner of the camera, and there's no way to really do that without a name.
A cell phone number is also a good idea, as it can't be (easily) tracked to your address, but still allows for fast, flexible communication.
If you can fit it, email address might also be a good idea, or a webpage if you have one. This opens up all kinds of ways that the person could track you down, hopefully to give you your camera back.
Beyond that, there's plenty of information you probably shouldn't include. Date of birth, home phone and address, things along those lines can allow people to track you down in a way well beyond what is necessary to return your equipment to you. Use common sense.
Some people feel the need to include a reward for the camera's return, hoping to help honesty along a bit. While this is hardly a requirement, there's an increased chance of a return, which to some people is worth the monetary loss. (Not to encourage potential thieves, of course.)