Winfried Nöth’s book has a great section discussing codes and I recommend that folks go out and buy it instead of reading it where I’ve pasted it in below.

I grabbed my copy from Google Books.

Code1Code2Code3Code4Code5Code6Code7Code8Code9Code10Code11Code12Code13Code14Code15Code16Code17Code18Code19Code20Code21Code22Code23Code24Code25Code26Code27Code28Code29Code30