So in the argument discussed in this topic, OP picking up a paper wallet worth 0.6btc, is this a theft scenario?
It wasn't theft because there were no bitcoins at all. It's a scam attempt in disguise designed to make you lose your money instead.
It's a question of what is the moral thing to do if such a thing happened for real. That's where the community has different opinions. Some wouldn't do a thing because it's not their coins. Others would "give" the original owner some time and then sweep the coins to one of their addresses. But the owner doesn't even know that the clock is ticking. Some users would try to warn the owner that their keys are compromised by depositing a small sum and then withdrawing it showing they have access to the private keys...
The answer to the question from a moral point of view, the person who found paper wallet will have a difference depending on whether he has morality or not. Some will take bitcoin for themselves (immediately or after a while), others will try to tell the owner to move it. It seems to me that on this forum, most of the users will lean towards the second, because, as I think, the majority here are decent and highly moral people. I have such an opinion.
A small inconsistency. The method by which people who have gained access to the wallet may not work if the wallet owner doesn't check the balance of his wallet or does so very rarely. I mean, he just might not know about the messages sent to him. Of course, it's worth trying and you can sign the bitcoin transaction with a message for this.