N.H. Rev. Stat. Ann. § 264:5

Security furnished in compliance with the requirements hereof shall be applicable only to the payment of a judgment against the depositor for damages arising out of the accident in question in an action at law in a court of this state begun not later than 2 years thereafter; and such deposit, or any balance thereof, after the expiration of such 2-year period, shall be returned to the depositor or his personal representative unless the department shall have received a written notice from the aggrieved person or his representative that suit has been brought.