three, going, coming, visiting
參 centers on the number three and the idea of joining or moving between places: three, going, coming, and visiting. The visiting sense extends naturally from coming and going.
參 is the traditional form of 参. It originally depicted three stars in the constellation Orion, representing the number three. The lower 彡 may have been added to emphasize the idea of joining or mixing, which later extended to coming and going.
The top part looks like a stylized three, and the lower 彡 suggests movement or joining. Picture three people coming and going, visiting each other.
For サン, think of the sun (サン) shining on three people as they come and go visiting: sun -> サン, and the three visitors are under the sun.