The use of HTML in alt.discuss is a highly debated topic. Some people are all for it, others absolutely hate it. Most of the groups in alt.discuss are HTML friendly.
It is recommended that you read the Charter for the particular newsgroup you are planning on posting in to see what their HTML policy is. For links to Charters see the "Welcome to alt.discuss" post.
A lot of people use the "10 Second Rule" which is if a post takes more than 10 seconds to load, they skip past it. Therefore, it is recommended that you use a quick loading sig in the User that you plan to post from.
Music in your sig can cause problems for some WebTV boxes, especially RA (RealAudio) files. RA files can cause a WebTV box to lock up and you get stuck in the post, or sometimes turn a box off altogether. In most groups it is considered rude to have automatic music in a post. A clickable link to your choice of music is recommended.
If you are interested in learning how to use HTML there are numerous alt.discuss groups available with friendly people who are willing to teach you and direct you to sources for tutorials, pictures and music.
If you do choose to use pictures (called gifs and jpgs) or music (called wavs or RealAudio) PLEASE make sure you do not steal it from the site. It costs some people actual money every time their site is accessed. Think about how many times one post of yours will be read, then multiply that by how many posts (and e-mails) you send, and the amount can be astronomical.
So if you choose to place a picture or music in your signature box, please either Transload it to your own website, or if you don't have one, to the website of a friend. There are a few websites set up for WebTVers to link from (Draac's being one) but it is _not_ the norm. For more information on this subject go here: http://www.geocities.com/~by2000/badlink ing.html Paul Erickson's page "The Trouble With Linking".
Posting in Usenet is a totally different story. Usenet is TEXT ONLY unless you are posting to a specific binary group. It will say "binary" in the name of the group. Many WebTVers get flamed and killfiled (where the computer user sets it up so they never see your posts) because of the HTML in signatures.
Comps are very different from WebTVs. Some people pay by the hour, and HTML takes a long time to load. Others have older computers, and the HTML will literally Crash them.
On the "Community" section of the sidebar on your HomePage it says
"Bulletin board postings Share opinions, pictures, and music in thousands of Usenet discussion groups."
This is something we are trying desperately to get WebTV to re-write as it is totally erroneous information. Please, when posting in Usenet, post from a User with no HTML in the signature box.
Enjoy the newsgroups and have fun!