countersign
1. coun.ter.sign \-.si-n\ n 1: a signature attesting the authenticity of a document already signed by a nother 2: a sign used in reply to another; specif : a military secret sign al that must be given by one wishing to pass a guard 2. countersign \.kau.nt-*r-'sig-n*-.chu.(*)r, -ch*r, -.t(y)u.(*)r\ vt 1: to add one's signature to after another's to attest authenticity 2: CONFIRM, CORROBORATE - coun.ter.sig.na.ture n