I know there was a request earlier for the addition of a reply between the lines style parser where only the stuff between some delimiters would be posted, dropping all the signatures, etc. See https://meta.discourse.org/t/reply-by-email-requires-reply-at-top/16983/28
I would love to see that implemented, as our marketing team wants people using large, remote graphic signatures with links, and it looks terrible when they get posted. I also have the same concern as most of my sales teams have their phone and other contact in their signatures.
I would even be happy if we just said you have to add the standard "-- " line before your signature, I can teach people to add that without much of an issue. It won’t fix everyone, but it seems simpler than trying to use regex matches to figure out every signature variation.