This was what my wife was planning on doing. But I think that runs the same risk as writing their name on their back. It's easily identifiable. The dog tag thing is probably the best idea. I don't think my son with take his wrist band off, he likes it too much. That's why I was hoping CM's could just scan it and get our reservation info.
It was also helpful to be told that standard procedure for CM's is to take them to baby care. So if they can't get a hold of you, you know where to find them.
I would imagine, unless a child is abducted, that a CM will find them eventually. I wonder what causes a CM to notice a lost child and take action though. My child is young enough he wouldn't walk up to anyone and tell them he lost his parents. I don't think we'll have a problem, though. They're just thoughts.
I distinctly remember a trip we took, I think it was our honeymoon, where I saw a maybe a 6 year old girl, alone, standing in the middle of a crowd screaming at the top of her lungs "I want my mommy." I assume she caught the attention of a CM and was hopefully reunited. But I didn't think much of it then, now that I have a little one, I imagine that would have been just as scary for the parents not knowing where she was.