Add Your Name Alongside Another's on Paperwork

This page is the CodyCross answer for the clue below from Concert Hall, Group 589, Puzzle 2 (Acoustic Design).

Question is: Add Your Name Alongside Another's on Paperwork

and the answer is: COSIGN

Word Meaning:

COSIGN — To sign a document jointly with another person, sometimes as an endorsement.

Definitions from Wiktionary.