Very rare mark WP #54 that's been imprinted in the glass, so that the mark is recessed deeply into the seal.

I think there are only a couple of examples of this kind in inset stamp in this mark WP #54.

The float itself measures about 3 1/2 inches in diameter, which is a little bigger than the floats stamped with the typical WP #54 mark.

This float has excellent provenance. It was beachcombed on Kunashir Island, Russia by Olga & Dmitry Solova.