Abstract: Described is a device comprising a retro-reflective marker comprising a core comprising a body portion, and a mounting recess extending into the body portion. The mounting recess comprises one or more flexible interior engagement structures configured for snap-on engagement with one or more complementary exterior engagement structures of a mounting post. The flexible interior engagement structures are configured so that when the retro-reflective marker is mounted onto the mounting post by direct axial application, the flexible interior engagement structures are deflected by the one or more complementary exterior engagement structures as the flexible interior engagement structures move past the one or more complementary exterior engagement structures and spring back to a relaxed position to thereby engage the one or more complementary exterior engagement structures so that the retro-reflective marker is mounted in a secured configuration on the mounting post.