Undocumented maker's mark that is one of the Sa series of marks.

This mark is similar to WP #125 Sa サ Shi シ except there is a line above the shi symbol.  So, this mark could be called Sa サ Shi シ Ichi 一.

There have been a few a examples of this mark to surface in recent years.

The float measures about 3 inches in diameter.  It's also almost completely frosted.

Beachcombed on Kunashir Island, Russia.  Kunashir is one of the four major Kurile Islands just north of Japan.