Saturn: Rectangle/Cube (The platonic Solid of Earth), Hexagram
Mars: Upward pointing Triangle/ Tetrahedron (The symbol of/ Platonic Solid of Fire)
Sun: Swastika, Sphere, Hexagram, 8-pointed Star, Circle, Sphere. Triangle, Tetrahedron
Mercury: Hexagram, Octahedron
Venus: Pentacle, 8 Pointed Star, hexagram, Shri Yantra
Moon: Circle, Sphere, Icosahedron, Shri Yantra
Jupiter: Shri Yantra, Doddecahedron, Sphere
The planets have many overlapping qualities, therefore more than one geometric shape can be assigned to them.
You can also create an individual symbol for a planet by combining different forms into one yantra.
An upward pointed triangle in the centre of a hexagram indicates the Sun.
The Hexagram is a combination of two triangles, Male and Female, Shiva and Shakti, Consciousness and Energy. The six rays indicate the 6 planets, while the centre is the 7th, the sum of all the other planets.
The triangle indicates the element of Fire and the prevalence of the male/Shiva aspect.