Good question, Father Bronze. The practice of linking to someone else's image is called "bandwidth-stealing" and it's generally frowned upon for the reasons listed above. Yes, it's best to upload the image to your own site. Make sure it's public domain before you do, though! A good place to find public domain fantasy images is at:
http://ftp.sunet.se/pub/pictures/fantasy/
There's a lot of older AD&D/Dragon Mag pics in there, as well as some by fantasy authors and illustrators. It's a good place to start looking.
I think Ziroc's only stip on the signatures is that they need to be small (under 10K in size) and not so big that a person on a 640 x 480 screen has to scroll back and forth to see the image (and all the accompanying text!) A lot of viewers still sign in on "pay-per-hour" systems.
Thanks,
[This message has been edited by Sazerac (edited 05-04-2001).]