I've been struggling with this too.  Got a hint from Scott and I think I did it, at least for my
system.  I believe I operate in Windows 95 and am using Netscape 4.1.  Here's what I did.
 
First go into WORD and create the autosignature you wish.  Do not use bold, color or any other
enhancements.  Then,
 
"Save as"
Give file a title
At bottom of menu where it says "Save as type," select "text only."
Then, save the file.
 
Now, go to your Netscape mail Inbox folder
"Edit"
"Preferences"
Open "Mail Groups" to see the subheadings
"Identity"
Up pops your email card.  At the bottom click on "Choose"
Click on "C" drive
Then "My docs"
Locate the autosignature file you created and double click.
Your email card should return and show the path to your autosignature file.
Close
 
To see if you succeeded, open "new Message."
Your autosignature should appear at the bottom of the bland email page.
 
Mine did.  See below  (Note that it includes my location)
 
--
Marlo
Merritt Island, Florida
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