37 C.F.R. § 2.194 – Identification of trademark application or registration.

(a) No correspondence relating to a trademark application should be filed prior to receipt of the application serial number.
(b) (1) A letter about a trademark application should identify the serial number, the name of the applicant, and the mark.
(2) A letter about a registered trademark should identify the registration number, the name of the registrant, and the mark.