The Collaborative International Dictionary of English v.0.48:

Superscription \Su`per*scrip"tion\, n. [L. superscriptio. See
   Superscribe.]
   1. The act of superscribing.
      [1913 Webster]

   2. That which is written or engraved on the surface, outside,
      or above something else; specifically, an address on a
      letter, envelope, or the like. --Holland.
      [1913 Webster]

            The superscription of his accusation was written
            over, The King of the Jews.           --Mark xv. 26.
      [1913 Webster]

   3. (Pharm.) That part of a prescription which contains the
      Latin word recipe (Take) or the sign ?.
      [1913 Webster]

WordNet (r) 3.0 (2006):

superscription
    n 1: an inscription written above something else
    2: the activity of superscribing

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "superscription":
   address, banner, banner head, billhead, caption, destination,
   direction, drop head, dropline, epigraph, hanger, head, heading,
   headline, jump head, legend, letterhead, motto, name and address,
   overline, postal zone, rubric, running head, running title,
   scarehead, screamer, spread, spreadhead, streamer, subhead,
   subheading, subtitle, title, title page, zip code, zone