Superscribe
/suːpəˈskɹʌɪb/
verb
To write on the exterior of, the surface of, or above.
“He superscribed each character with its Latin-alphabet equivalent.”
To write (something) on the exterior of an object, such as a document or an envelope.
“His wife superscribed her own notes on each of his letters before sending them in packets to the editor.”
To address (an envelope etc.).