Q: How can I get a "signature" on my postings?  On mail?

A: These are actually two separate questions.

To get an automatic signature on netnews postings, create a file named
.signature (dot signature) in your home directory.  (Use an editor for this--
see the 'u' menu, use 'ce' to pick an editor, then 'e' to edit the file.)
Note that the news software will reject .signatures > 4 lines long (to save
net bandwidth; people were getting a little too obnoxious on the signatures).

To get a signature on mail, you need to convince your mail program to do it.
The "normal" mail program doesn't know how.  The 'elm' mailer, 'nr' on the
comm/mail menu, does, IF you edit elm's configuration file (.elm/elmrc)
and add "set signature = ~/.signature".  (If you put in a different filename
elm will use that, of course.)  Also, do a 'help' on 'nr' (man on elm) to
find out more, like local vs. remote signatures.