How are the FEMA Xs significant in the novel, The Floating World?

The white Xs spray painted on the houses symbolize, in Joe’s words, “the mark of the destroying angel” (108). These Xs are Federal Emergency Management Agency (FEMA) search codes. The left side identifies the rescue team that visited the house; the top indicates the date and time of the team’s arrival; the right side lists codes for hazards encountered within the structure; and the bottom indicates the number of living and/or dead people found inside. Joe inverts a biblical analogy, then, since, in Exodus 12:23, the destroying angel passes by marked houses, whereas Hurricane Katrina has visited marked houses.