This undocumented mark is comprised of the Hiragana symbol 'Ha' は oriented at a 90 degree angle to a roof.

This unique Ha は mark is the only example known to exist in collections.   I think this is an extremely rare float that needs to be preserved for history.

The float itself measures 48 inches in circumference or about 15 1/4 inches in diameter.

It shows lots of signs of use which may indicate that it's an older float, possiblly pre-WWII.

This float was purchased in Japan.  The seller said that he had held this float for about 20 years.  He had received it as a gift from a fisherman in Noto, Japan.