37 CFR § 1.5 - Identification of patent, patent application, or patent-related proceeding.
(a) No correspondence relating to an application should be filed prior to receipt of the assigned application number (i.e., U.S. application number, international application number, or international registration number as appropriate). When correspondence directed to the Patent and Trademark Office concerns a previously filed application for a patent, it must identify on the top page in a conspicuous location, the application number (consisting of the series code and the serial number; e.g., 07/123,456), or the serial number and filing date assigned to that application by the Patent and Trademark Office, or the international application number of the international application, or the international registration number of an international design application. Any correspondence not containing such identification will be returned to the sender where a return address is available. The returned correspondence will be accompanied with a cover letter, which will indicate to the sender that if the returned correspondence is resubmitted to the Patent and Trademark Office within two weeks of the mail date on the cover letter, the original date of receipt of the correspondence will be considered by the Patent and Trademark Office as the date of receipt of the correspondence. Applicants may use either the Certificate of Mailing or Transmission procedure under § 1.8 or the Priority Mail Express® procedure under § 1.10 for resubmissions of returned correspondence if they desire to have the benefit of the date of deposit in the United States Postal Service. If the returned correspondence is not resubmitted within the two-week period, the date of receipt of the resubmission will be considered to be the date of receipt of the correspondence. The two-week period to resubmit the returned correspondence will not be extended. In addition to the application number, all correspondence directed to the Patent and Trademark Office concerning applications for patent should also state the name of the first listed inventor, the title of the invention, the date of filing the same, and if known, the group art unit or other unit within the Patent and Trademark Office responsible for considering the correspondence and the name of the examiner or other person to which it has been assigned.
(b) When the letter concerns a patent other than for purposes of paying a maintenance fee, it should state the number and date of issue of the patent, the name of the patentee, and the title of the invention. For letters concerning payment of a maintenance fee in a patent, see the provisions of § 1.366(c).
(c) Correspondence relating to a trial proceeding before the Patent Trial and Appeal Board (part 42 of this title) are governed by § 42.6 of this title.
(d) A letter relating to a reexamination or supplemental examination proceeding should identify it as such by the number of the patent undergoing reexamination or supplemental examination, the request control number assigned to such proceeding, and, if known, the group art unit and name of the examiner to which it been assigned.
(e) [Reserved]
(f) When a paper concerns a provisional application, it should identify the application as such and include the application number.