N.Y. Elec. Law § 8-708
The early mail voter shall mark an early mail ballot as provided for paper ballots or ballots prepared for counting by ballot counting machines. They shall make no mark or writing whatsoever upon the ballot, except as above prescribed, and shall see that it bears no such mark or writing. They shall make no mark or writing whatsoever on the outside of the ballot. In cases where the express intent of the voter is unambiguous, any stray marks or writing shall not be a basis for voiding a ballot. After marking the ballot or ballots they shall fold each such ballot and enclose them in the envelope and seal the envelope. They shall then take and subscribe the oath on the envelope, with blanks properly filled in. The envelope, containing the ballot or ballots, shall then be mailed or delivered to the board of elections of the county or city of their residence.
N.Y. Elec. Law § 8-708