The graffiti seems to remind Walter that the hotel doesn’t actually exist in a magical, remote utopia: it’s part of a larger society and, as such, is just as susceptible to the violence, suffering, and chaos that plagues the rest of the world. Walter’s comment about Paul acting weird reveals that Paul’s story, too, leads to the Hotel Caiette. If Walter’s insinuation that Paul is responsible for the graffiti is correct, this would make sense, as Paul seems to have a tendency toward self-destructive behavior, and vandalizing one’s place of work certainly fits into this category.