25 U.S. Code § 10 - Employee to sign letters
The Commissioner of Indian Affairs, with the approval of the Secretary of the Interior, may designate an employee of the Indian Office to sign letters of that office requiring the signature of the commissioner or assistant commissioner, and all signatures of such employee while acting under such designation shall have the same force and effect as if made by said commissioner or assistant commissioner.
Section is from the Indian Department Appropriation Act, 1910.
For transfer of functions of other officers, employees, and agencies of Department of the Interior, with certain exceptions, to Secretary of the Interior, with power to delegate, see Reorg. Plan No. 3 of 1950, §§ 1, 2, eff. May 24, 1950, 15 F.R. 3174,64 Stat. 1262, set out in the Appendix to Title 5, Government Organization and Employees.