This is a relatively rare set, and I took an iphone photo of the photograph by Michel Arnaud in Mah Jongg The Art of the Game, published by Tuttle.  The caption in the book, page 90, reads: "The Chinese Game Company in Baltimore made this rare set of hollow tin tiles. The tiles are conservative in design, but the counters are very colorful. The box lid is a typographical triumph."

The visible Flower tiles are the four callings: fisherman, wood cutter, farmer and scholar. You can see Bams, a few Dots, and the Craks. There's a mystery in the Craks-and who will crack it open? What's wrong? One eagle-eyed reader pointed it out to me the other day.

And the answer is: The 6 Crak has the Chinese number for 9, and although you can't see it, the 9 Crak has the number for 6!