We do not remove user signatures.
Since there is no standards around user signatures, there is no easy way to even get it to work for 75% of the emails.
The best solution I’ve found so far requires machine learning and lots of training samples. It gets much harder when you have to support more than one locale…
EDIT: I already added support for italian replies, but did push a new version of the gem. I just did, you should update 
https://github.com/discourse/discourse/commit/480e8d0dc7c5627b36ad3151719c67780fa3c5b6