Source : Webster's Revised Unabridged Dictionary (1913)

Signor \Si*gnor"\, Signore \Si*gno"re\, n. [It. See {Seignior}.]
   Sir; Mr.; -- a title of address or respect among the
   Italians. Before a noun the form is Signor.

Source : WordNet®

signor
     n : used as an Italian courtesy title; can be prefixed to the
         name or used separately [syn: {signior}]