A nice post about some of the Tango's code and elements of etiquette, with lovely illustrations: from Los Angeles Tango Academy's blog.
This is one of my favorite: don't give feedback during the Milonga...
Illustrations: © Les Pas Parfaits, Dessins Véronique Paquette (I warmly recommend you to have a look at their lovely work)
The illustrations are lovely and it reminds me of other really lovely tango illustrations, just have a look at Emilie Boudet's website... such a good eye!