Between the ninth and sixteenth centuries, crests (mon) evolved from ornamental motifs to potent signifiers of social and political identity. Japanese warriors borrowed the use of stylized decorative motifs from the aristocracy, eventually transforming them into full-fledged heraldic markers. Scholars have explained this evolution in fundamentally military terms: absent uniforms, mon enabled warriors to distinguish friends from foes on chaotic battlefields. Yet twelfth- to fourteenth-century representations, in war tales and illustrated scrolls, reveal that the diffusion of mon accelerated in peacetime. Growing attention to mon in sources largely reflects the narrative logics of the various genres: mon served to commemorate battlefield deeds rather than organize military action. Indeed, the impetus for their diffusion was genealogical ‒ a manifestation of the contemporaneous restructuring of warrior society around the corporate warrior house (ie). The ie came to represent the fundamental unit of affiliation for Japanese warriors, with its emphasis on shared ancestry and its hierarchy of lineages and sub-lineages. Mon served as powerful visual markers of the unity and flexibility of these new kinship and political groups, providing a language to represent minute variations of identity and status in a society keenly attentive to both.