Use a thicker block under the piston, it makes getting the clip inserted easier. I made my block from full one inch thick hardwood back around 1970, still using it but have a couple of those red plastic jobs now that come with the ring compressor sets.
I have about 9 years on you.
That symbol looks like rings that have no ring keepers, many vintage saws had small round ports so the rings would not catch in them, those did not need the ring keeper pins in the piston. The black area may indicate the allowable ring end gap, not certain and someone else may have a different take on that.
It is an Ancient Chinese Taoist symbol representing the universe's duality.
