To be effective, posting must be done according to specifications outlined on the New Hampshire Fish & Game site. Excerpt:
Under state law (RSA 635:4), the legal manner of posting calls for posting durable signs with any words describing the physical activity prohibited, such as “No Hunting or Trespassing,” in letters at least 2 inches high, and with the owner’s name and address. The signs shall be no further than 100 yards apart on all sides of the property and shall also be posted at gates, bars and all commonly used entrances.
Signs should be placed every 300 feet and at entrances. Estimate the perimeter of your property and divide by 300 feet to determine how many signs you need. If you have a plot plan for your property, it likely includes boundary measurements. Google Earth also includes a ruler tool for measuring distances.
If you wish to allow hikers on your property, cross out the words, “Trespassing for Any Purpose.”
Once your land is posted, it is illegal for anyone to be on your property without your permission. Contact your Conservation Officer to report any unlawful activitiy.