Wouldn't this be very vulnerable to scamming in itself though?  It's trivial to, say, parse the top 10,000 receiving addresses from the blockchain that hold the most value at this moment.  What's to stop a scammer from taking a coin that's marked as "stolen" and transferring a single satoshi to each of these top 10,000 mostly valid addresses?  Wouldn't everyone just be marked bad at that point?

Remember, there's no way to "deny" a transaction.  Anyone in possession of coins that had been annotated as bad could go on to cause lots of trouble for other people very easily.