46 C.F.R. § 201.126
If service of subpoena is made by a United States marshal or his deputy, such service shall be evidenced by his return thereon. If made by any other person, such person shall make affidavit thereto, describing the manner in which service is made, and return such affidavit on or with the original subpoena. In case of failure to make service, the reasons for the failure shall be stated on the original subpoena. In making service the original subpoena shall be exhibited to the person served, shall be read to him if he is unable to read, and a copy thereof shall be left with him. The original subpoena, bearing or accompanied by required return, affidavit, or statement, shall be returned without delay to the Administration, or if so directed on the subpoena, to the presiding officer before whom the person named in the subpoena is required to appear.
46 C.F.R. § 201.126