Classic examples of comics as propaganda include the early Captain America comics.
A modern example of comics being used as propaganda include "Chick Tracts", which try to convince the reader to become a Christian.
Odds are that anyone living in a city has seen a Chick Tract, so you'd know how they try and make their message understandable.
(Before you ask, I don't believe in God. I used to, but I stopped shortly after my mother died.)