This is the name of a course that I took around 1980 at MIT. This course is all electrical engineering and analog systems, and in Bits and Things we abstract any analog properties from the real circiuts and only consider their logic and timing is always synchronized to a clock signal.
To consider systems in all their generality I have come to understand that we need a much more thorough understanding of signs and semiotics. Peirce is so far ahead of his time that much of this important work lies neglected. Also worthy of attention is 20th century thought on cybernetics and later biologists such as Maturana nd Varrella who introduce the idea that all biological systems are networks of self-sustaining processes, naming this class autopoetic. A productive use of Peirce' three aspect signs would be to describe the processes of living beings in their environments. The structural coupling that maintains the self-other boundary and constitutes its way of being in the world is best described with signs.
Here's the signals and systems part, each signal that the living being (autopoetic system) uses to maintain itself, each transaction of its structural coupling, eating, mating, fighting, escaping and other elements for plants or fungus for example is going to have a sign or more likely many signs associated with it. There will be a physical expression of the sign, the signal (first aspect) that signals (second apsect, green is green relative to red and other colors, this is the relative aspect). The third aspect is the key one, the signal means something to the living being. It says to run or to chase or to hide, to sprout, to flower, and so on. Living systems inherit a lot of survival wisdom not just into individual species, but throughout the Gaian system over some four billion plus years. This history did not result in digital binary computers except in the sense that one of its descendants, humans, invented them out of abstract thought and logic. This all builds on our natural language heritage but is a highly distinct development. I happen to find talk of thinking computer, strong AI, to be naive or premature at best. To be sure computers do and will do many more things that we used to think of as requiring "human intelligence", and they will do many routine tasks and expand what they do by making the space of what is routine or controlled larger. If we do acheive strong AI it will require a much deeper understanding of living systems and their intelligences and wisdom than our quite immature race. It is arrogance to think otherwise. There may or may not be a God, but I know I'm not the smartest thing in the universe.