Icon: I guess the picture will be small, but if possible, a picture of some lines that looks like how the lines of the planets look when you set Earth to center. Or perhaps the trail of the Moon as it looks like when orbiting the Earth and the Sun is set to be the center.
Name: Center of Trails/Orbital Center
Description: All trails are drawn relative to (the) [name]. If (the) [name] is set to be a star in a star system simulation, you will see elliptical trails of the planets, asteroids and comets orbiting the star. The moons of the planets will make trails that look curly, since they orbit the planets while they orbit the star.