It is esthetically extremely displeasing.
Perhaps a script could be written to automatically erase double signatures?
How would that be checked anyway?
For example, it's relatively simple to check for the following:
John Doe
John Doe (Noble)
and then remove the first John Doe. I believe that the autosignature is there, among other reasons, to prevent someone from signing as the following:
John Doe, the Grand Warthog Master Chief of Covenant Slaying Badassery
And attempt to pass that off as a legitimate title. Of course, that's an extreme case, but the point is that it prevents people from claiming false titles (Something that would have had dire consequences in Medieval times...which hasn't really changed in modern times either)
But how sensitive do we want it? How does the script know when something is intended as a signature, and not a part of the letter? What if someone doesn't use any known closings (Sincerely, Yours Truly, Best Regards, etc)
So how would the game tell the difference between the following:
Dear Idiot,
This is a message about how stupid you are.
John Doe
versus the following:
Dear Idiot,
This is a message from the person named after this sentence.
John Doe
It's a lot of work for something that I think is rather stupid to waste time trying to code. How many people would really care that you can't sign your name manually? On the other hand, if we do away with the autosignature, how many people do you already know will jump on the opportunity to call themselves something they're really not.