How to make Mail use standard signature separator? I am using many signatures under Mail.
I noticed that unlike many professionnal E-mail programs Mail
doesn't automatically include the standard E-mail signature separator.

The command:

defaults read com.apple.mail | egrep '(--|sep|sig)'


didn't let me a lot of hope.

Is there any way to configure Mail so that it will automatically include the standard separator -- \n with any signature ?
You need to manually add the sig-dashes, --\n, to the top of your signatures within Mail.app:


Mail (menu) > Preferences > Signatures


It may be possible to automate the changing of signatures, see How to change/customize mail signature in Mountain Lion? for details of Mail's signature file format.