countersign (
http://definr.com/countersign)
n 1: a secret word or phrase known only to a restricted group;
"he forgot the password" [syn:
password,
watchword,
word,
parole]
2: a second confirming signature endorsing a document already
signed [syn:
countersignature]
v : add one's signature to after another's to attest
authenticity; "You must countersign on this line of the
contract"