individual words/signs are quite arbitrary

I found something quite interesting talking about ASL (American Sign Lang.) that would contribute quite well to an argument about how the individual words/signs are quite arbitrary. It talked of how individual ASL signs have meaning within a system of signs, not to individual pictures. So, I guess the sign for Tokyo doesn't relate directly to a picture of Tokyo.
This may be quite obvious, but how many of us realize that the lexical items we are using, be they spoken or signed, are only understood within the context of the system we are using them, understanding of language, through language. If we have more knowledge of the system, we are better able to understand the parts within a system. I guess it's a 'chicken and the egg' kind of realization I'm making here. However, suddenly it has dawned on me that the way I look at words sometimes, is like I expect that the words immediately create certain connections to pictures within student's minds. Yet as in the Fromkin book, students need to start making connection to other words they have already acquired. Beginners often need more input and understanding of the system that they are learning (time to make those connections). After immersion into the language, and getting comfortable (by making those lexical connections between words) they may be ready to understand. I’m probably going off on another tangent here. But, the arbitrariness of the sign language example set me off thinking about how words, along with grammar (signs and facial expressions) are a tools within a system, called language.