https://www.merriam-webster.com/thesaurus/countersigning
COUNTERSIGNING Synonyms: 19 Similar Words | Merriam-Webster Thesaurus
Synonyms for COUNTERSIGNING: endorsing, signing, signing on, registering, cosigning, signing up, inking, subscribing, inscribing, scrawling
merriam webstersynonymssimilarwordsthesaurus