I shot the image in a mirror by available light. Sized it in Photoshop, added text, etc. Once you have created your graphic, you simply use a web page designer to make a link around it. If you know even basic HTML you can make a link. Otherwise, simply type HTML directly into this forum page to make it work. Use square braces instead of pointy braces to surround your HTML.
Once you have it laid out satisfactorily, you copy the HTML into your personal information page at Nikonians. There is a spot at the bottom for a signature, and you can drop HTML in there. Every post will then be signed by that HTML.
BTW, my little logo below is an F4. I have used it awhile. I have taken a new image with my D100 and will redo my logo soon. Here's the new image: