cult, showing radical (no. 113)
礻 is a radical form used in characters related to religious rites, worship, or showing respect to deities. Its standalone meaning is tied to cult or ritual display.
礻 is the radical form of 示, which originally depicted an altar or a stand for offerings, associated with showing or displaying to spirits.
The shape resembles a simplified altar with a top surface and a supporting leg, used for showing offerings in a cult ritual.
For シ, imagine a priestess (し, a simple Japanese word for female priest) performing a ritual at the altar: し -> シ.