Considering the sign as motivated.
"To the semiotician, a defining feature of signs is that they are treatedl by their users as 'standing for' or representing other things." 55
"In the S model, the signified is only a ... mental construct." 58 - and so constructed by a material person in context - and so motivated.
Modality 62 - comes into play when we consider Photographs As Signs.
The Treachery of Images, 1936
Chandler recounts how 'commonsense' tends to join signifier and signified in non-arbitrary ways 69-70. Pre-school children arguing that sun and moon could not be changed, for instance. "for the child, words to not seem at all arbitrary." He refers to this is a "confusion of representation." The invention of written language and other developments separated reference from referent, which signifiers are subject to conventions different than their references - and their authors. 71. It's the separation from authors that might be interesting here.