27 C.F.R. § 31.116
The registration of an individual proprietor shall be signed by the proprietor, the registration of a partnership shall be signed by a member of the firm, and the registration of a corporation shall be signed by a duly authorized officer thereof; however, any individual, partnership, or corporation that is a proprietor may appoint an agent to sign on the proprietor's behalf. The person signing the registration form must identify his or her signing capacity as "individual owner," "member of firm," "agent," or "attorney-in-fact," as appropriate, or, in the case of a corporation, by the title of the signing officer. A receiver, trustee, assignee, executor, administrator, or other legal representative who continues the business of a dealer by reason of death, insolvency, or other circumstance must indicate the fiduciary capacity in which he or she acts. Registration forms signed by persons as agents or attorneys-in-fact will not be accepted unless, in each instance, the principal named on the form has executed a power of attorney authorizing that person to sign and that power of attorney is filed with the TTB officer with whom the TTB Form 5630.5d is required to be filed. Form 5630.5d must be verified by a written declaration that it has been executed under the penalties of perjury.
27 C.F.R. §31.116
26 U.S.C. 6061 , 6065