N.H. Rev. Stat. § 260:68
Service of such process shall be made by leaving a copy thereof with a fee of $2 in the hands of the director or in his office, and such service shall be sufficient, provided that notice thereof and a copy of the process are forthwith sent by registered mail by the plaintiff or his attorney to the defendant, and the defendant's return receipt and the affidavit of the plaintiff or his attorney with compliance therewith are appended to the writ and entered therewith. In the event that the notice and copy of process are not delivered to the defendant the superior court may order such additional notice, if any, as justice may require. In the event that the notice and copy of process cannot be delivered to the defendant because he was deceased at the time of the accident or thereafter, the notice and copy of process shall be sent to the executor or administrator of the deceased defendant's estate, if one has been appointed. If no executor or administrator has been appointed, the plaintiff may petition the superior court for the appointment of a guardian ad litem for such deceased defendant, and upon appointment of such guardian ad litem, the notice and copy of process shall be sent to such guardian ad litem.
RSA 260:68
1925, 106:1. PL 100 :33. 1929, 73:1. 1933, 104:2. 1941, 156:1. RL 116:43. RSA 264:2. 1967, 268:1. 1981, 146:1, eff. Jan. 1, 1982.