Source : Webster's Revised Unabridged Dictionary (1913)

Subsign \Sub*sign"\, v. t. [imp. & p. p. {Subsigned}; p. pr. &
   vb. n. {Subsigning}.] [L. subsignare; sub under + signare to
   mark: cf. F. soussigner. See {Sign}.]
   To sign beneath; to subscribe. [R.] --Camden.