[coconino]

I wondered about this too, understanding the convention to be newline-dash-dash-space with an optional LF. If you want to strip sigs based on a convention then it would seem sensible to either stick to the actual one. My only caveat is that many people use a spaced double dash in plain text to stand for a spaced en- or em-dash, so these would need to be considered.

OTOH, few people know to bother to properly prefix their sig, so it may all be wasted effort.