Amendment to Allege Use (AAU)
A sworn statement signed by the applicant or a person authorized to sign on behalf of the applicant attesting to use of the mark in commerce. With the AAU, the owner must submit one specimen showing use of the mark in commerce for each class of goods/services included in the application, and the required fee.
AAUs must be filed before the date the examining attorney approves the mark for publication in the Official Gazette.
You should check the status of the application before filing the AAU to make sure that is timely. An AAU filed after the mark is approved for publication but before a notice of allowance has been issued (during the "blackout period") is untimely and cannot be accepted.
Source: U.S. Patent and Trademark Office.