What is the difference in the terms "signal return", "signal reference", and "signal ground"?
"Signal ground" is the most generic of these terms. It is used primarily when you want to distinguish it from other kinds of ground, such as safety ground or power supply return paths.

"Signal return" means that the speaker is thinking particularly about how the signal current is flowing. This would come up when thinking about EMC in terms of loop area (magnetic coupling). This could apply to cables or PCB designs, and primarily in low-impedance circuits.

"Signal reference" means that the speaker is thinking particularly about distinguishing the signal voltage from any kind of common-mode interference. This would apply primarily in high-impedance circuits.

But they all mean "ground" in one sense or another, and the specific nuance depends very much on context.

These nuances come up when you realize that, in real-world designs, you have to treat "ground" not as a single, universal reference node, but rather as a network of nodes connected by various parasitic impedances (resistance, inductance) to each other and to other circuit nodes (capacitively or inductively).