I don't know about you, but I have misplaced cameras in the past. Never really lost them, just forgotten one somewhere (in a classroom, usually).
That is a terrifying feeling. I start freaking out and hyperventilating, wondering where I could have left it, and if someone might have taken it.
Ken Rockwell always says that with most cameras, the photographer uses them for a couple years, heck, even a couple decades, and then sells the camera. Because of the strong possibility of selling a camera eventually, I don't want to engrave my information on it, but I also don't want to leave it unmarked.
Enter the Dog Tag.
I had four of these made up from a company called DogTagsOnline.com. The tags, ball-chains, and black rubber silencers cost me $17 total, shipped to my place First Class Priority Mail.
I tossed one on my camera bag, one on the D300's ring, one on my neck, and I've still got one to spare.
Now if I misplace a camera, or have it disappear on the spoiler of a Dodge Neon, I am confident that if a decent person finds it, it can be returned to me!