This article says that shortly after the portraits were reported as being removed, Kim visited a military unit near the DMZ. It's impossible to know what the motives behind it were and the article doesn't really try to guess. But the trip does provide some interesting scenarios. Did Kim visit the unit because he was worried about their loyalty or at least wanted to reaffirm it? Was the move part of a larger motive to regain some respect and good will from the military? Probably not, the visit was most likely routine. As Bob said, the removal of the pictures themselves probably aren't significant either. After all, why would anyone wanting to start a coup begin by removing the leader's portraits from a couple public buildings? However, since we know that support for the Dear Leader is limited at best, I suppose a coup or at least the threat of one isn't out of the possibilty.