When I first bought this float I thought it had the symbol 'mizu' 水, but when I showed it to a friend they told me that it was the symbol 'Ei' 永. Ei 永 is an undocumented mark that translates to mean 'eternal'.
This float measures 20 1/2 inches circumference or about 6 1/2 inches.
It has excellent provenance having been found on the beaches of Kwajalein Atoll in the Marshall Islands by Bill Hadley.