The sign is for "Loudon's Ford / British and Continental / army ford protected / August - September 1777 / by Generals Enoch Poor / and Benedict Arnold".
A Flickr friend did a bit of research on the precise location and importance of Loudon's Ford; as little as could be found, it does raise the question of why Gen. Schuyler's name isn't on the marker, as it was apparently his preparations for the fight against Burgoyne that saw the need to hold the mouth of the Mohawk.
Pure speculation, but one can assume it picked up the name of Loudon's Ford (or Ferry) from the Earl of Loudoun, perhaps as part of his preparations for the attempted seizing of Louisbourg in 1757. It is for him that Loudonville is named.
Today, Enoch Poor is nearly as obscure as the location of Loudon's Ford.