I see the Hawaii overprint notes that are short snorters selling for $30-$50 depending on condition. For a regular silver certificate, I'd guess more like half that. However, this note suggests it could be commemorating a Navy ship crossing the equator during the war (google Navy equator crossing for more info). The possible WWII Navy linkage probably increases the value even though it isn't verifiable provenance. If there is mention of a ship name on the note, that would help with your research.