"the bond between the signifier and the signified is radically arbitrary"

Ok so I am going to try and make some sence out of "the statement the bond between the signifier and the signified is radically arbitrary" (35). So first off the signifier is the sound or image we get when someone uses language. The signified is the concept or idea you get when you hear or see this image. In structuralism you cannot have one without the other. So for example when you hear the word cat you think of its opposite dog. They are both arbitary or random from each other. Structuralist Theory says that you cannot think language with thinking about the opposite such as sun and moon. One does not exist without the other. When trying to think of a show that would display this theory I trying to think of a show that had two opposite characters and I came up with Midsummer. In that show we have Theseus and Hippolyta. Theseus is a represented by night and Hippolyta by day. There are many quotes in the text that use qualites of day and night to descibe them. Each character would not have the same dynamic power without he other one yet they are random opposites.
When you throw Post-Structuralist into the mix it really just throws everything off. In this case signifier is never signified because nothing you get from the text is ever correct. It is an endless line of unstable questions to be asked about what the literature is saying. It just keeps defering the "morals" that you see in structuralist theory. Honestly I have no examples for this in the theatre world. If any theater geeks out there had any examples I would love to hear from you!