“Not at this address - return to sender” doesn’t do much, but “Deceased - return to sender” always works for me. Hopefully someone at the bank/sender flags the account and makes it the account holder’s problem.
(Don’t use sticky notes, they’ll fall off in the mail. Use a black permanent marker and write as big as possible so that they can’t “accidentally” miss your note. Cross out any barcodes or other markings that the post office adds so that it won’t automatically be re-sent to you, the machines will reject it and it will be manually routed back to the sender)
The warrant gives them the legal right to enter the house, but being vampires, they cannot enter without being invited. However, should you decide not to invite them, you can be found in contempt and arrested, which then creates the problem that the vampire police officer can’t enter to arrest you without being invited…