I don't get the point of your response, but I was trying to illustrate that even though the earth ground symbol was common to represent earth ground, chassis ground and signal ground up to the 1930's (at least in the US), a separate signal and chassis ground symbol was needed just for circuits...
You can have two different "grounds" in a circuit -- the safety or earth ground (such as from a power a power supply), and a signal ground. Consider a 2-rail amplifier requiring +/- power. The signal ground may be floating above the earth ground (or chassis ground), and would need to use...