A Sign may itself have a “possible” Mode of Being. E.g. A hexagon inscribed in or circumscribed about a conic. It is a Sign, in that the collinearity of the intersections of opposite sides shows the curve to be a conic, if the hexagon is inscribed; but if it be circumscribed the copunctuality of its three diameters (joining opposite vertices.) Its mode of Being may be Actuality: as with any barometer. Or Necessitant: as the word “the” or any other in the dictionary. For a “possible” Sign I have no better designation than a Tone, though I am considering replacing this by “Mark.” [—] An Actual sign I call a Token; a Necessitant Sign a Type.
http://www.commens.org/dictionary/entry/quote-letters-lady-welby-21