Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
Whistle post
Modern whistle posts are of simple sheet metal construction, utilizing a 'W' marker. Some multiple crossings protected by a single sign have an 'X' displayed below the 'W', other multiple crossings may have 2 or 3 W markers on the same post.