The symbol that first comes to mind for me is a Celtic triquetra. It's had a special place in my life over almost 20 years now and often returns to mind. I have shared its meaning to a number of people in my real life too, as it speaks some truth to me about the nature of life. I am on my mobile just now and am not able to upload an image. If I can, I will come back later and post the image then. But first I will share its meaning.
The symbol is a circle with three interwoven loops inside it coming out from the centre. It stands for three realms of existence that are equally interlinked to form the whole. These are: the heavenly realm, the earthly realm and the realm of the underworld. All are integral to our experience. This reminds me that there is light in life, as well as darkness, and that we all walk the earth with its groundedness in between.
Thinking of this meaning, I feel better able to accept all the shades that have made up my life, from pain and trouble, to heightened moments of happiness and joy, as well as the more mundane, ordinary aspects of daily life that help keep the others in balance. This speaks to my personal spirituality, which also embraces life as a great mystery.
If anyone is curious to see the symbol, just search 'Celtic triquetra' on Google. There are various interpretations of its meaning. The one above is the one that most moves me.
I also have Irish ancestry, which I researched thoroughly some years ago. Celtic spirituality is therefore meaningful to me as part of the ancient origins of my DNA.
I really love this discussion thread for the thoughts and feelings it is inspiring us to share. Thanks to all who are contributing. 
