I actually first loved this for the beauty of the water and loneliness of this bobbing post (I think a navigational marker, but perhaps a dinghy sighted straight from the rear view?) Then I looked closer and saw the simply painted "BUTT." Which made me laugh. And seems just right in many ways.
5 1/4" x 3 5/8". Excellent condition, sharp and crisp, c. 1940s.