I am not arguing how justified is Cuban embargo. There are more evil countries in the world, that have relationship with US. But, as far as official USA policy prohibit communication with Communist Cuba, using the Cuban posters and symbols demostrate lack of respect to the US government. How could you expect people respect our government, if the leading candidate to the president does not respect it.
You do not agree to the government policy - fight it by all legal means. But, do not jeopardize the legal system but openly breaking rules!