Cats, dogs, and other mammals are known to mark their territories in myriad ways, but pet owners in Brussels have discovered a more enduring and inviting method. What began as a single project by artist Ingrid Schreyers spurred a municipality-wide initiative: the government of Schaerbeek, a suburb bordering the city of Brussels, now installs any mosaic, either created by residents or a local artist, free of charge. Many people are choosing portraits of their furry companions, although the idiosyncratic designs range from playful depictions of wildlife to urban scenes.