14 CFR 49.13 - Signatures and acknowledgements.
(a) Each signature on a conveyance must be in ink.
(b) Paragraphs (b) through (f) of § 47.13 of this chapter apply to a conveyance made by, or on behalf of, one or more persons doing business under a trade name, or by an agent, corporation, partnership, coowner, or unincorporated association.
(c) No conveyance or other instrument need be acknowledged, as provided in 49 U.S.C. 44107(c), in order to be recorded under this part. The law of the place of delivery of the conveyance determines when a conveyance or other instrument must be acknowledged in order to be valid for the purposes of that place.
(d) A power of attorney or other evidence of a person's authority to sign for another, submitted under this part, is valid for the purposes of this section, unless sooner revoked, until -
(1) Its expiration date stated therein; or
(2) If an expiration date is not stated thereon, for not more than 3 years after the date -
(i) It is signed; or
(ii) The grantor (a corporate officer or other person in a managerial position therein, where the grantor is a corporation) certifies in writing that the authority to sign shown by the power of attorney or other evidence is still in effect.