Corvo Signs Registry at Boyle Party is a written note found in Dishonored.
It's undoubtedly not worth your time and I hesitate to even mention it, but apparently on the night of the Boyle Party someone signed the guestbook as "Corvo Attano". It must be a perverse joke, surely. However, you asked to be notified of all such matters, and in truth we never located the Royal Protector's body, so I thought best to bring it to your attention. Sorry for troubling you with this matter. I know Lady Boyle was dear to you.
An alternate note will appear if Corvo chooses the nonlethal elimination and signs the guestbook.