The Commens Dictionary
Quote from ‘Adirondack Summer School Lectures’
A sign is something which is in a triadic relation to two things being a sign of a object for an interprete. Its relation to its object is such as to determine the sign while producing little or no change in the object. As we usually say, the object is agent, the sign patient. There must actually be an object; at least, the sign must actually be affected by an object. But is is not essential that it should be more than fit to have an interprete. In order that the sign may actually function as a sign it must have an interprete but it is not essential that it should so function. It may suffice that it is fit so to function. Toward its interprete the sign is agent, the interprete patient. That is the sign essentially affects the interprete without being much affected itself. The relation of the sign to its object may be only dyadic, though in the case of symbols it is triadic. But the relation of the sign to its interprete is essentially triadic and consists in determining the interprete to a relation to the object corresponding to the relation of the sign itself to that object. In fact the interprete usually becomes itself a sign of the object for a possible interprete.
This passage comes from a portion of the Adirondack lectures that has been misplaced in the microfilm edition of Peirce's manuscripts