Law in Australia suggests I can be charged with 'theft by finding' if I don't make a reasonable attempt to identify the owner. This seems to be impossible in this instance... seems a shame to hand it in to police.. who are likely not educated enough to know what to do with it. What would you do?
Australia is making a lot of crazy laws about crypto in recent years to ban exchanges from providing "privacy coins" e.g. ZCash, monero, so I wouldn't be surprised if this is one of them.
I wouldn't hand it over to the cops, some insider might just swipe the balance from the real owner.
Perhaps you can send a small amount (e.g. $5) to the address corresponding to that private key, and then transfer it out back to the source address to alert the real owner that their paper wallet has been found!
Perhaps make an OP_RETURN transaction with a thousand satoshis or so, that says: "This paper wallet has been found on a beach. If you own this address key, get your coins out immediately!" It can be viewed on such block explorers as Blockstream, that decode the OP_RETURN data.