This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
銿 combines 金 (metal) with 甬, which likely contributes the sound. The exact historical development is uncertain, and the character is rare in modern Japanese.
With 金 (metal) on the left and 甬 on the right, 銿 might suggest a metal object, but its meaning is uncertain. Picture a mysterious metal artifact with an unknown purpose.
For ショウ, imagine showing (ショウ) someone the mysterious metal artifact: show -> ショウ, and the metal 金 hints at the object.