N.H. Rev. Stat. Ann. § 477:47

Conservation, preservation, and agricultural preservation restrictions are interests in real estate and a document creating such a restriction shall be deemed a conveyance of real estate for purposes of RSA 477:3 and RSA 477:3-a relating to execution and recording. Such a restriction may be enforced by an action at law or by injunction or other proceeding in equity. No grantee or contingent grantee interest in such a restriction shall be created or amended by any document unless it bears the notarized signature of the grantee and any and all contingent grantees.