On many TLK-related materials like comics, books, etc. that's interesting because this symbol wasn't shown in TLK trilogy.
Bronies may know Spiral Sun - it's Zecora's cutie mark because she's African and this is an African symbol.
What it means? "The ancient spiral, thought to represent life, death, and rebirth, as the cycle of the sun, is incorporated in this version of the sun, a universal symbol of energy and light shared by many world cultures."
So that mean that this is nothing less, nothing more than a symbol of the Circle of Life!
Of course I knew that Sun controls the Circle of Life, but now I know that not only controls - the Sun IS the Circle of Life
First frame of TLK = Sun = Circle of Life
PS. I know that somehow it's sounds stupid, but I'm not English native-speaker and believe me - it sounded better in my native language, in my head. I just can't describe good enough what I mean in English.