mark, print, impression
迹 centers on a visible trace left behind: a mark, print, or impression that shows something was there.
迹 combines 辶 (movement) with 亦, which likely contributes the sound and the idea of a footprint or trace. The exact historical development of 亦 in this context is uncertain.
The movement radical 辶 wraps around 亦, like a path showing where someone walked. Picture a trail of footprints: each mark is a 迹.
For セキ, imagine a detective saying 'I see a key mark!' while examining a footprint: 'see key' -> セキ, and the mark is the trace.