All documented vessels must have their ID numbers displayed on a clearly visible, structural part of the interior of the hull. As boat designs have changed over the years, especially production boats such as Hunter, Catalina, Beneteau, etc., the large wood placards aren't necessarily what you want if you choose to display the number in your cabin (it can also be displayed in a cabinet or locker if it is clearly visible when those are open).

A sleek, brushed stainless steel documentation placard designed to meet Coast Guard standards

The numbers meet the required 3 inch height and are permanently fused to the surface of the stainless steel with a laser. They won't scratch or fade over time.

The placard measures 15 inches wide by 5 inches high. It can be purchased with holes for #6 screws but to meet USCG requirements it must be mounted permanently, which precludes mechanical mounts like screws.