This article is from the Advertising on Usenet FAQ, by Joel K. Furr firstname.lastname@example.org.
A .signature is a mini-file that is automatically appended (stuck at the
end of) to any Usenet messages that you post -- regardless of what the
content is. Whether or not you can create and use a .signature depends on
what sort of system you're using to access Usenet news. Many UNIX systems
simply require you to create a file called ".signature" in your root
directory within your shell account and put whatever you want your
.signature to say within that file. Other systems, like America Online,
allow you to do something similar, but the implementation varies from
system to system. If you can't figure out if your system supports a
.signature, ask the people in charge for help.
Typically, it is considered bad manners to put more than four lines of
information in your .signature, regardless of what those four lines might
say or contain. Gigantic ASCII pictures of dragons, for example, are
annoying when you have to see them every time a certain person posts.
Similarly, it's considered bad manners to put an advertisement in your
.signature and then post a lot of empty or nearly-empty articles simply
to get your .signature into various newsgroups.
On the other hand, if you post meaningful, responsible messages in groups
you're actually interested in, and those messages happen to have the
address of your Web page tacked on at the end, few people will complain.
Just keep .signature advertisements extremely short and sweet. Let your
Web page contain the sales pitch -- the .signature should usually be
little more than a listing of your URL and perhaps a mention of what sort
of business you're in.
Restraint and responsibility are everything -- if you've got those, people
will sit up and listen to you.