White Castle mug RARE BLUE with built in ashtray

White Castle coffee mug RARE BLUE and white! Thick walls on this vintage little coffee mug. The mug measures 3 1/4" X 2 3/4", stamped Mayer China, Beaver Falls, PA Interpace USA This unique mug has a built in ashtray on the bottom of the mug! From the 1960’s. Excellent vintage condition, still shiny.