Saussure: dyadic model of a sign: composed of a signifier (form of the sign) and the signified (concept communicated by the sign.) This excludes the object, referring only to the concept of the signified.
Peirce: triadic model of a sign: composed of representamen (form of the sign,) interpretant (the effect of the sign on the viewer,) and object (to which the sign refers.) The object determines the sign, but only certain relevant features of the object are to be included.