Source : Webster's Revised Unabridged Dictionary (1913)

Superscribe \Su`per*scribe"\, v. t. [imp. & p. p.
   {Superscribed}; p. pr. & vb. n. {Superscribing}.] [L.
   superscribere, superscriptum; super over + scribere to write.
   See {Super-}, and {Scribe}.]
   To write or engrave (a name, address, inscription, or the
   like) on the top or surface; to write a name, address, or the
   like, on the outside or cover of (anything); as, to
   superscribe a letter.

Source : WordNet®

superscribe
     v 1: write on the top or outside; "superscribe one's name and
          address"
     2: write on the outside or upper part of; "superscribe an
        envelope"