31 C.F.R. § 1010.914 – Service of summons.

(a) Who may serve. Any delegate of the Secretary authorized under § 1010.912 of this chapter to issue a summons, or any other person authorized by law to serve summonses or other process, is hereby authorized to serve a summons issued under this chapter.
(b) Manner of service. Service of a summons may be made—
1. (1) Upon any person, by registered mail, return receipt requested, directed to the person summoned;
2. (2) Upon a natural person by personal delivery; or
3. (3) Upon any other person by delivery to an officer, managing or general agent, or any other agent authorized to receive service of process.
(c) Certificate of service. The summons shall contain a certificate of service to be signed by the server of the summons. On the hearing of an application for enforcement of the summons, the certificate of service signed by the person serving the summons shall be evidence of the facts it states.