My former (and current) avatars are Celtic.
Here are some details on the older, more complex one:
It is a triquetra (purple) inside an interlaced circle and triangle. It came from Wikipedia:
More generally: https://en.wikipedia.org/wiki/Triquetra
And here, relating 'skelos' back to Greek: https://en.wikipedia.org/wiki/Triskelion
Please note that someone else entirely is @triquetra!