The mark consists of a three dimensional, visible exterior configuration of a hollow mounting bracket defined by left and right halves having identical but mirror-image-reversed appearances that cooperate to form a generally rectangular upper end region, a downwardly pointed lower end region, and a hollow, forwardly extending central region situated between the upper and lower end regions and provided with C-shaped access openings on opposite left and right sides thereof beneath which are provided upwardly-facing shelf-like surfaces that extend forwardly-rearwardly at equal heights adjacent the widest part of the mounting bracket, and with each of the upper and lower end regions defining a forwardly opening, centrally located mounting hole.