The Collaborative International Dictionary
Countersign \Coun`ter*sign"\ (-s?n`; 277), v. t. [imp. & p. p. Countersigned (-s?nd`); p. pr. & vb. n. Countersigning.] To sign on the opposite side of (an instrument or writing); hence, to sign in addition to the signature of a principal or superior, in order to attest the authenticity of a writing.
Wiktionary
vb. (en-past of: countersign)
Usage examples of "countersigned".
But it takes a presidential order and even then it has to be countersigned by Security.
The act is countersigned by the Chief, and you know that an act countersigned by the Chief is absolutely irrevocable.
The document authorizing the Last Trump was countersigned by the Chief, and you know that it is irrevocable for that reason.
Lincoln knew that Stanton had countersigned McClellan's direction to Halleck to arrest Grant if he resumed the habits that had caused him to quit the army years before.
Even more astonishing was that it was countersigned across the bottom: Adolf Hitler, Fuhrer und Reichskanzler.
All the orders that you write on any patient must be countersigned by myself or one of the two interns on the service, whom you will meet presently.
If you write orders in the ICU they have to be countersigned the moment you write them.
Orders for patients on the ward can be countersigned en masse at various times during the day.