名詞 counter-sign:

1. a secret word or phrase known only to a restricted group
   同義詞：password, watchword, word, parole, countersign
2. a second confirming signature endorsing a document already signed
   同義詞：countersignature, countersign

動詞 counter-sign:

1. add one's signature to after another's to attest authenticity
   同義詞：countersign