WP #300 'Ue 上 with Ichi under Roof' stamped on a 2 1/2 inch float.
WP #300 is an uncommon stamp on 4 inch floats. This example is 2 1/2" in diameter, so I'm assuming it could be more rare.
Perfect stamp with all points clearly represented.
This glass ball was found in the Tohoku region in Northern Honshu Island, Japan.