I guess I'm sitting in the position of, if somebody dropped $20 out on the course, and you're stumbling around the woods and come across it, are you going to call the number and ask if they want it back if it has one on it? Not the best example, I know, but I see it as much the same.
If the name is somebody I know, definitely I'll give it back.
If the person comes up and says its theirs after I get it, definitely give it back.
If I find it in a stream where with ice still on the edges and a 20 foot vertical bank to get down to it, and it's visible from the top of the bank, I'm not going to worry about it.
If it is worth it to them, the person will find it. I am a very firm believe in this, and I don't truly see how you can say you just can't find it. I've spent many hours rummaging through poison ivy and nettles looking for my discs. I keep looking because it is worth it to me to find them. If its a disc I don't care about I'll say "**** it, lets keep playing."
EDIT: I guess I don't see the whole name/number on the disc being completely valid. I've seen several people on the course with sharpies specifically to write their names on a disc as soon as they find one. I've seen it done on blind throws. I don't take it as meaning it is theirs.
I hope you never cone to my home course. Let me know which one is yours will you. That way I won't play there.
It is called common courtesy and integrity. Something I am finding less and less of. What a sad world we sometimes live in.