According to a former Arizona Secretary of State and auditor they are looking for watermarks that are not supposed to be there. Arizona assures them the ballots "do not" have watermarks. More of a just in case. Ehh... who really knows until they release all the information.
The short interview in this article may be illuminating.
https://www.thegatewaypundit.com/2021/05/former-arizona-secretary-state-confirms-four-six-truckloads-voting-machines-handed-back-maricopa-county-yesterday/
According to a former Arizona Secretary of State and auditor they are looking for watermarks that are not supposed to be there. Arizona assures them the ballots "do not" have watermarks. More of a just in case. Ehh... who really knows until they release all the information.