(3)
Assertion by payment of the small entity basic filing or basic national fee. The payment, by any party, of the exact amount of one of the small entity basic filing fees set forth in §§ 1.16(a), 1.16(b), 1.16(c), 1.16(d), 1.16(e), or the small entity basic national fee set forth in § 1.492(a), will be treated as a written assertion of entitlement to small entity status even if the type of basic filing or basic national fee is inadvertently selected in error.

I think that the answer is “assertion of small entity status.” If a party pays the exact amount required for the small entity basic filing fee or small entity basic national fee, the PTO treats the payment as a written assertion of entitlement to small entity status. Therefore, no signature from anybody is required in this case.

This takes you to MPEP 1820 Signature of the applicant.

PCT Art. 14 will let you know that the RO will check for the presence of a signature.

Rule 4 informs you that generally all applicants need to sign (and all inventors if the relevant Member Country so desires, such as the US).

However, things have changed for IA filed from Jan 1, 2004, and Rule 26.2bis tells you that actually the signature of just one applicant will do afterall.

Further, the request may be signed by an agent instead (with pre-2004 IA requiring appointment via a separate Power of Attorney that again does have to be signed by applicants).

Explained in more detail under the heading “Signature of Applicant or Agent” under 1820.

There is another question from the Forum regarding signatures. – question regarding signature in box IX of of the IA filing (who can sign and what authorization is required)

“§ 41.67 Appellant’s brief
(a)(2) The brief must be signed by the appellant, or the appellant’s duly authorized attorney or agent and must be accompanied by the requisite fee set forth in § 41.20(b)(2).”

If the appeal brief is not signed, the relevant form paragraph states:

Ҧ 12.112 Brief Defective РUnsigned
The appeal brief filed on [1] is defective because it is unsigned. 37 CFR 1.33. A ratification properly signed is required. To avoid dismissal of the appeal, appellant must ratify the appeal brief within ONE MONTH or THIRTY DAYS from the mailing of this communication, whichever is longer. Extensions of time may be granted under 37 CFR 1.136.”

Also note that a notice of appeal does not require a signature, but MPEP 1204 does state:

“… failure to sign the notice of appeal may have unintended adverse consequences; for example, if an unsigned notice of appeal contains an (unsigned) authorization to charge the notice of appeal fee to a deposit account, the notice of appeal will be unacceptable because the notice of appeal fee is lacking.”

While an assertion claiming small entity status by paying the exact small entity basic filing or basic national fee does not require a signature, a written assertion of small entity status does require a signature by:

“37 CFR § 1.27(c)(2) Parties who can sign and file the written assertion.

The written assertion can be signed by:
(i) One of the parties identified in §1.33(b) (e.g., an attorney or agent registered with the
Office), § 3.73(b) of this chapter notwithstanding, who can also file the written assertion;
(ii) At least one of the individuals identified as an inventor (even though a § 1.63 executed oath or declaration has not been submitted), notwithstanding § 1.33(b)(4), who can also file the written assertion pursuant to the exception under § 1.33(b) of this part; or
(iii) An assignee of an undivided part interest, notwithstanding §§ 1.33(b)(3) and 3.73(b) of this chapter, but the partial assignee cannot file the assertion without resort to a party identified under § 1.33(b) of this part.”

Also note that loss of entitlement of small entity status DOES require a signature by a party identified in § 1.33(b) (assertion by payment of other than small entity fee not sufficient).

“37 CFR § 1.27 (g)(2) Notification of loss of entitlement to small entity status is required when issue and maintenance fees are due. Notification of a loss of entitlement to small entity status must be filed in the application or patent prior to paying, or at the time of paying, the earliest of the issue fee or any maintenance fee due after the date on which status as a small entity as defined in paragraph (a) of this section is no longer appropriate. The notification that small entity status is no longer appropriate must be signed by a party identified in § 1.33(b). Payment of a fee in other than the small entity amount is not sufficient notification that small entity status is no longer appropriate.”