N.H. Rev. Stat. Ann. § 104:3

A sheriff may appoint so many deputies as he thinks proper, by deputation in writing, under his hand and seal, and not otherwise, who shall be sworn to the faithful discharge of their duties. The deputation and certificate of oath thereon shall be recorded at length by the clerk of the superior court in a book kept for that purpose, and no deputy shall act as such until the record is made.