streamer
縿 refers to a streamer, a long narrow flag or banner used for decoration or signaling.
縿 combines 糸 (thread) with 參, which likely contributes the sound. The exact historical development is uncertain.
The thread radical 糸 suggests fabric, and the right side 參 looks like a flowing shape. Imagine a long streamer made of silk threads fluttering in the wind.
For サン, picture a sunny day with a streamer waving: sun -> サン, and the bright sun makes the streamer shine.