N.H. Rev. Stat. Ann. § 236:41

The state historic preservation office established under RSA 227-C shall consult with the commissioner of transportation on the marker program. Before placing any marker, the commissioner shall secure the state historic preservation office's approval of the marker, its location and its wording. The state historic preservation office shall make any investigation needed to obtain information on the event to be commemorated and on the appropriate location for the marker, including consulting historians and holding public hearings.