This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
珅 combines 王 (jade) with 申, which likely contributes the sound. The exact historical development is uncertain.
Since the meaning is unclear, focus on the shape: a jade-like 王 beside 申, like a precious stone with a name.
For シン, imagine a shiny jade stone: shiny -> シン, and the 王 on the left is the jade.