Would need to be an agreed-upon message encrypted with the vandal's private key.
1. Person wanting defacement would indicate the amount for the bounty, along with the message to be posted on the defaced property
2. Vandal contacts payer and agrees to conditions. He/she also gives the client their public key
3. Vandal performs defacement, then add the specified message to it, encrypted in his or her private key
4. Vandal notifies the person paying the bounty that the job is complete, sending him/her a picture of the defacement with encrypted message
4. Payer decrypts message, verifies it matches, then pays out the agreed upon bounty to the vandal
