You don't need a protocol change to do that if it's already possible to put your information in it.
Just change the extra information to
your name + previous block hash you've mined + sign(your name + previous block hash)
It should be possible to not insert this information so real anonymous mining stays possible.

That won't work but I wasn't suggesting a breaking protocol change but rather an agreed upon optional standard which is fully backwards compatible.

Instead something like pools (optionally) create a public private keypair used for signing (probably should have mechanism for revocation or replacement).
The pool would modify the getwork so that they hash some standardized identifer (should be specific to the block to avoid substitution attack) and sign it.

Yes I was indicating such a system should be optional but sites like blockchain.info could scan the block look for a signature and then verify it w/ the pool's public key.    In cases where the block can't be verified (or no signature is present) blockchain.info and other sites could still try to guestimate the origin by IP address.  As long as the signature is placed somewhere which isn't a breaking change uniformed clients would simply ignore it.

Did we figure this one out?

Key pair signing would also enable other things like enabling revocation of transactions. A method could be developed that would enable stolen coins to be recovered or made worthless.

Say a large amont of coins were stolen. If they had a private key assigned, an insurance transaction could be made for the same amount with a revocation key attached to invalidate the transfer after a lengthy confirmation period. As soon as the transaction hits the chain the addresses are block from transferring coins. This could also be challenged by doing another challenge transaction in the same way.  You could add in some security features like requiring a public ip address to broadcast during the entire revocation period to dispute. In that way the source could be traced. For a thief they would not be able to "afford" the chargeback or hide anonymously. It's not free per se to do either so it's not readily abuseable.