The Collaborative International Dictionary of English v.0.48:

Lettering \Let"ter*ing\, n.
   1. The act or business of making, or marking with, letters,
      as by cutting or painting.
      [1913 Webster]

   2. The letters made; as, the lettering of a sign.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Letter \Let"ter\ (l[e^]t"t[~e]r), v. t. [imp. & p. p. Lettered
   (-t[~e]rd); p. pr. & vb. n. Lettering.]
   To impress with letters; to mark with letters or words; as, a
   book gilt and lettered.
   [1913 Webster] letter bomb

WordNet (r) 3.0 (2006):

lettering
    n 1: letters inscribed (especially words engraved or carved) on
         something [syn: inscription, lettering]