The first sigs I recall seeing were disclaimers. Most people used to get on the net from school or work. In order to distance our opinions from those of our employers, we often added these things. I don't know if they had any legal grounding.

My first sig was "My employers don't tell me what to say and I don't tell them where to stick it."

A while later I changed it to "My employers disagree with everything I say, think, feel, do, or plan to do."

k