This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鉮 is a rare character combining the metal radical 金 with the phonetic 申. Its historical origin and original meaning are uncertain.
With the metal radical 金 and the phonetic 申, 鉮 might suggest a type of metal or metallic object, but its meaning is not established. Picture an unknown shiny metal piece labeled with the sound 'shin'.
For シン, imagine a shiny metal shin guard: shin -> シン, and the metal radical 金 reinforces the image.