N.H. Rev. Stat. Ann. § 436:94

Any equine in the state which reacts positively to an official test is hereby required to be tested a second time at the expense of the state; and, if the test reads positive a second time, the equine shall be so identified with a freeze marking 12A which shall be at least 2 inches high. Such marking shall be applied to the left shoulder or the left side of the neck of the reactor.