PTK is a triangle system. The triangle has multiple meanings: it represents the combat flow, timing, quartering the opponent in a triangle, attack angles, countering angles, footwork angles, the three attack energies, and the strength of the triangle in addition to PTK philosophy and values.
The missing points of the outside triangle represent the dynamic nature of the combat flow. You have to keep moving strategically using sound tactics, so you won't remain in one place - go DYNAMIC. The points are transitory.
Finally, the skull represents mortality, not death or evil. Since we are mortal, life and the preservation of life is supremely important. This is at the very heart of what SAPTK is about. SAPTK is about learning to protect yourself and those you care most about.