Pre-WWII float with maker's mark WP #30 'Kita 北 Shi シ', which means "North Four".  This corresponds the four Kurile Islands of: Kunashiri, Etorofu, Habomai, and Shikotan.

This float measures 8 1/4 inches in diameter.

Additional information from a well-respected collector:  "At the time of writing his first book, Walt had only seen that mark on 8 inch floats. It may be that 8 inch floats were all that were used in the area he was in when he found the mark. I have had the pleasure to own 2 floats with this mark. One was 9.5 inches and the other was 10.5 inches. Here is my 10.5 inch Kita Shi. I wish I had kept the 9.5 inch float but it was traded years ago. These two were the only two I've seen for sale in my years of collecting."