N.H. Rev. Stat. Ann. § 231:95

The department of transportation shall examine all railings, posts, or other warning signs or structures erected by a town upon any highway, upon the written request of such town, and if the same are approved as standard, a record of such request, of the examination and approval, and of the locations shall be made and kept in the office of the department. A copy of such records shall be filed forthwith in the office of the town clerk. When certified by the commissioner of transportation, a copy shall be received by all courts as evidence of the sufficiency of such railings, posts, or other warning signs or structures for a period of 3 years after such record has been made.