19 CFR 113.22: Witnesses required.

(a) Generally. The signature of each party to a bond executed by a noncorporate principal or surety must be witnessed by two persons, who must sign their names as witnesses, and include their addresses.

(b) Witness for both principal and surety. When two persons signing as witnesses act for both principal and surety, they must so indicate by stating on the bond “as to both”.

(c) Corporate principal or surety. No witnesses are required where bonds are executed by properly authorized officers or agents of a corporate principal or corporate surety. For requirements concerning the execution of a bond by an authorized officer or agent of a corporate principal or surety, see §§ 113.33 and 113.37 of this part.