Is the husband's signing of a "no objection to work" paper for his divorced wife, who is still within her 'iddah (waiting period) and living under his sponsorship, considered a return of her to his marital bond?

Revocation does not occur by your signing the letter; rather, it occurs during the waiting period (iddah) through an explicit statement, or an allusive statement that implies the meaning of revocation along with the intention, or through sexual intercourse, according to the more preponderant opinion.