According to Radio Free Asia:
The businessman, who spoke on condition of anonymity, said that high-ranking North Korean traders he dealt with “expressed self-esteem in relation to North Korea’s military strength” and told him, “regardless of U.N. sanctions, we [North Koreans have] never stopped reacting.”
“It’s hard to understand how high-ranking officials can adamantly deny North Korea’s responsibility for the sinking of the Cheonan while propaganda posters showing a ship being broken in half by a fist are in circulation,” he said.
Update: I am currently reading B R Myers' The Cleanest Race and this propaganda poster, if genuine, is a perfectly good illustration of one of his main points in the book. Up until now, North Korea's stance on the Cheonan issue has been to cry foul at the hostile Yankees and their South Korean puppets for conspiring to blame them for something they had nothing to do with. Korean Central News Agency even collated their own articles in a special section here. And when their Foreign Minister spoke about the incident following the United Nations' absolution of the North from any blame he said: The recent development in which the overall situation on the Korean Peninsula reached a point of explosion in a moment due to a conspiratorial farce once again reminds us of the danger of the present cease-fire and the urgency to establish a peace-keeping regime. The DPRK will make consistent efforts for the conclusion of a peace treaty and the denuclearization through the six-party talks conducted on equal footing.
However, B R Myers warns:
Too many observers wrongly assume that the (North) Korean Central News Agency's English-language releases reflect the same sort of propaganda that the home audience gets. In fact there are significant differences. For example, there the DPRK presents itself to the outside world as a misunderstood country seeking integration into the international community, it presents itself to its own citizens... as a rogue state that breaks agreements with impunity, dictates conditions to grovelling U.N. officials, and keeps its enemies in constant fear of ballistic retribution. Generally speaking the following rule of thumb applies: the less accessible a propaganda outlet is to the outside world, the blunter and more belligerent it will be in its expression of the racist orthodoxy.
In this case, the poster doesn't depict anything that could be called racist but the rest of Myers' analysis of North Korean propaganda seems to fit this episode to a tee.